La Jolla, California (CNN) To face each day, Claire Wineland undergoes hours of breathing treatments. It's a reality of living with cystic fibrosis she's come to accept.

But last month, as the nebulizer hummed loudly in her La Jolla, California, hotel room, she breathed in medicine through her mask and hoped this day would be the first step toward something different.

She'd traveled from Los Angeles with her mother, her best friend and her pit bull, Daisy, who flopped down on the floor atop one of Claire's ever-present oxygen tubes. A full day of appointments at a nearby medical center awaited her, when she would begin the evaluation process to see whether she might be a candidate for a double-lung transplant.

A year earlier, Claire vowed that she'd never have the major surgery.

"It's not for me and never has been," she said at the time.

She was more comfortable dealing with the illness she knew than taking on the unknown. She preferred to focus on leading a purposeful life than worrying about death and how to dodge it.

Claire Wineland sits in her hotel room with dog Daisy before heading to evaluations at the Center for Transplantation at UC San Diego Health.

A series of irreversible setbacks and some painful soul-searching, however, have prompted an about-face in her thinking. Claire, 21, needs new lungs, or she will die -- sooner than she's willing to accept.

The only question is: Did her change of heart come too late?

Feeling trapped

It wasn't as if the clouds parted and she suddenly saw the light. Claire's new outlook was the result of a messy and humbling self-reckoning.

She had long managed to push through physical discomfort to lead a life that mattered. After emerging from a 16-day medically induced coma at age 13, she envisioned the Claire's Place Foundation , which today provides financial support to struggling families affected by cystic fibrosis. She appeared in brutally honest viral videos in which she talked about topics like death and did it with a smile. Since she was 14, she had been taking to stages and wowing audiences with beyond-her-years wisdom. Along the way, she nurtured a love of travel.

She was wrapping up a three-city tour last fall when pneumonia landed her in a Philadelphia hospital for two weeks.

Doctors there sat her down and told Claire she had to stop flying. Period. They told her that her lungs could collapse and that she ran the risk of dropping dead on a plane, she said. They warned that it would be painful and laid out what it would feel like if an air pocket in her lungs burst.

"You will feel like you're being stabbed to death ... and then blood will stop flowing to your brain," she remembered them saying. "And I was like, 'OK, I got the message! Copy that!' "

She took a three-day train ride home and began to settle down.

Because her body works so hard to breathe, Claire must take in about 5,000 calories a day and relies on a feeding tube to absorb calories while she sleeps.

Cystic fibrosis affects more than 30,000 people in the United States (and more than 70,000 worldwide), according to the Cystic Fibrosis Foundation . The disease causes an overabundance of mucus, which traps infections and blocks airways in the lungs, complicates digestion, affects the pancreas and other organs and, eventually, leads to respiratory failure.

The median survival age is about 40, according to the foundation -- a great improvement from the 1950s, when surviving long enough to attend elementary school was rare.

Claire became uber-diligent with her care. She was on top of her dozens of medications, including her shots for cystic fibrosis-related diabetes, endured as best she could the feeding tube at night, even though it made her throw up, and spent extra time with her breathing treatments. For four hours daily, she said, she wore a vest to shake her lungs and loosen mucus. She also tried supplements like turmeric and found comfort in the nettle infusions she drank throughout the day.

But even with all of this, her lung function continued to decline. In one year, she said her working lung capacity fell 10 points -- from 35% to 25%. Short walks and visits to the beach left this lover of the outdoors exhausted. Simple grocery shopping became too tough to manage. She had no energy for local speaking engagements and lost her income flow. She felt homebound, trapped and unable to do what mattered to her most.

CFers, as she refers to people with cystic fibrosis, often talk about "the Wheelchair Decision" with dread, Claire said. But when breathing and getting around became too difficult and she got hers in February, it initially felt "like freedom."

With her best friend, Larissa, taking on the role of "designated wheeler," the duo could tool around outside. The day she got the wheelchair, they went on a seven-hour adventure around Los Angeles' Venice Beach, where Claire lives, visiting the canals, going to the park, soaking in the ocean breeze.

And while most of the time, she has no qualms about needing a wheelchair, there are accessibility issues, the sidewalks are a mess, and she can't be pushed through sand. Inevitably, she's had those moments when she thinks, "It sucks that I need this. It's painful that it's gotten this far."

Claire breathes in medicine through a nebulizer as Larissa pounds her back with cupped hands to help loosen mucus in her airways.

Then Claire, who's undergone more than 30 surgeries and been in the hospital a quarter of her life, received another jolt during a March hospital stay. Medical staff discovered that her portacath wasn't working. The small dome under the skin of her chest provides a central line into a vein, allowing easy administration of IV treatments -- such as antibiotics, which she must take regularly to beat back constant infections. A portacath replacement means surgery, and Claire's pulmonary function was -- and remains -- at a level too dangerous for her to go under anesthesia.

Though the portacath was fixable, Claire didn't know it would be at the time. A wave of terror washed over her. She fell apart and realized it was time to take the transplant idea seriously.

"I can't go under anesthesia. I can't fly. I can't do anything," she remembered feeling with a panic. "I have completely locked myself in a position of not being able to do anything besides die."

Ready for the race

After leaving the La Jolla hotel, Claire was wheeled into the Center for Transplantation at UC San Diego Health, prepared to meet with members of the lung transplant team.

She'd eaten a McDonald's McGriddle sandwich the day before -- a secret she employs to put on an extra pound or two before weigh-ins -- just in case they asked her and her 95-pound frame to step on a scale. She was armed with questions and a notepad, ready to studiously record all she'd learn. Since she'd been here less than two years earlier and decided against pursuing the transplant path then, she was eager to tell them why this time was different.

A nurse who serves as the lung transplant coordinator, Megan Serletti, spent several hours educating Claire, her mom and Larissa about the process.

Megan Serletti, top, a nurse who works as a lung transplant coordinator, leads Claire and her mom, Melissa Nordquist Yeager, into the transplantation center.

They talked about the battery of tests that would determine whether she would qualify to get on the waiting list, some of which Claire knew well and described as "gnarly." They discussed the lung allocation score, the number Claire will get if she's approved that measures how sick she is and determines where she sits on the priority list.

They discussed what life on a waitlist looks like: the necessity that she stay within a four-hour drive of the center, the importance of not ignoring phone calls, the exercise she'd need to grow stronger and the multitude of blood draws and exams she'd have on her schedule.

"We call a transplant your marathon," Serletti said. "We tell people to train for your marathon. The day you get called is the day of the race."

There were forms to sign and questions she'd need to consider. For example, would she be willing to accept lungs from a prostitute?

"I'm fine if a donor had sex in exchange for money," Claire quipped. "Way to bring the hustle."

How about from someone who was an IV drug user and contracted hepatitis C, a condition that is treatable?

"Honestly, I'd just laugh if I got new lungs and caught something else," she said. "I already have the body of someone who's been around the block."

Serletti spoke of the realities after surgery, including the drugs Claire would need to take for the rest of her life, the physical and emotional challenges she might face, the changes in lifestyle she'd have to honor.

Claire wrote everything down. She curled her legs into the chair, revealing the tattoo on her left ankle: the thumbs-up "Don't Panic" logo from "The Hitchhiker's Guide to the Galaxy."

"None of it spooked me," Claire said afterward, over lunch in the transplantation center's courtyard. "Now that I'm looking at it as something I have to do, I don't care about any of the side effects. I'm willing to deal with anything."

'We both just started crying'

To qualify for new lungs, a person must be sick enough to need a transplant yet strong enough to withstand the surgery and recovery.

There were 1,436 candidates for lung transplants as of April 20, according to the United Network for Organ Sharing , which manages the nation's organ waiting lists. Of those, 122 had a primary diagnosis of cystic fibrosis. Last year, of the total 2,449 lung transplants performed, CFers accounted for nearly 11% of the recipients.

Unlike previous introductory meetings, when her heart wasn't in it, Claire takes in every word during this education session about lung transplants.

A lung transplant is not a cure, but it can extend a life, if all goes well.

Of those who received lung transplants (not just CFers), dating to 2000, an average of 84% survived after one year, nearly 54% survived five years, and slightly more than 30% survived 10 years or more, according to the organ sharing network's data.

Deciding to go for a lung transplant, let alone a double-lung transplant (the only option for CFers), is no small matter.

Claire first visited a transplantation center at UCLA when she was 14 but said that was too early for the idea to make sense for her. At 17, she checked out the program at Stanford University but was turned down, her mom explained, because they could tell that Claire wasn't interested. She checked out the option again, at the very place she had returned to now, when she was 19.

While her peers were being tasked with picking out prom dresses or decorating dorm rooms, she was being asked to contemplate her mortality.

She prayed that she'd want it as much as she knew her parents and doctors did, but her heart wasn't in it, she said. She was still happy with what she had and, as an adult, able to make her own decisions.

Her parents, who split up when Claire was 3, struggled to make peace with her choice.

"Just think of it as insurance, even if you don't want to do it," her mother, Melissa Nordquist Yeager, pleaded at first. "Get on the list so you can change your mind."

But ever since she'd been a small child, Claire had a sense of self, an understanding of her condition and a sort of intuition Yeager needed to trust -- even if it made her uncomfortable.

Her dad, John Wineland, said Claire "has a relationship with her body that is sacred" and described his daughter's thinking: "This is the body I came in with. This is the body I'm going out with."

And as her parent, he said, "I have to live with it."

Claire was born with cystic fibrosis and has spent a quarter of her life in the hospital. (Family Photo)

To see her struggle and deteriorate over the past year was both sobering and excruciating for them. So when Claire broke down and said she'd changed her mind, they were thrilled, excited and terrified.

"I was blown away, so grateful, happy and hopeful. It was a sign that she wasn't willing to give up," remembered Yeager, who was with Claire at the hospital in March and heard the news first.

"I called her dad, and we both just started crying," Yeager said.

"I'm just praying my ass off, really, that everything goes smoothly, that she can get a shot at more time on the planet," Claire's dad said. "There are a lot of hoops she has to jump through to be accepted."

'Are you ready?'

It's not uncommon for CFers to change their minds about transplant, social worker Leslie Fijolek assured Claire.

Fijolek, who serves on the transplant team, remembered Claire from the last time she visited UC San Diego Health. Fijolek's job is to think about "who are these [new] lungs going to live with," she said, get a sense of the care system recipients have in place and provide support to make the process successful for everyone involved.

Is Claire compliant in taking her medications? Is she prepared to relocate near the transplantation center, where she'll need to be for at least three months after the transplant if she gets one? Who'd move with her and drive her to appointments?

"How's your mood been? Any depression and anxiety?" Fijolek asked.

Leslie Fijolek, a social worker, asks Claire hard questions to see whether she's prepared to take on what a transplant would mean.

Claire mentioned how her decline, starting last fall, threw her into a depression. They talked about how she'd lost the ability to manage her physical decline, how she'd like to find a therapist who works with patients facing chronic illness, how she turns to arts and crafts projects to get out of bed -- and out of her head -- on rough days.

Photos on a cell phone are passed around, showing the papier-mache tree she's been working on and how the bark and surrounding foliage are remarkably true to life.

Fijolek turned serious, locked eyes with Claire and said what everyone in the room already understood: "You know you need a transplant."

"I was so young. I was so naïve," Claire answered, describing where she was before. "All the side effects used to scare the shit out of me. My relationship to transplant and all it entails has changed."

Fijolek, who was all too familiar with Claire's past ambivalence, pushed her further.

"Let's say you got listed in about two weeks; it means you can get a call at any time," she said. "Are you ready?"

Claire assured her she is.

"It's a big change from where you were," the social worker said.

"I didn't want to waste anyone's time," Claire answered.

Her mother sat by, fanning herself with a medical brochure, listened and wiped a tear from her eye.

All she had

The last appointment of the day was with one of the transplant team's pulmonologists.

Dr. Kamyar Afshar explains the importance of Claire building her strength so she can handle the transplant, if she's given one.

Dr. Kamyar Afshar got down to the nitty gritty. He wanted to know what antibiotics still worked for her, how many bowel movements she has a day and the last time she coughed up blood.

"Two days ago," she told him. "It's usually one or two times a month."

He prescribed walks every day to build up her endurance and suggested she increase her continuous oxygen flow from her normal 2 liters per minute to 6 liters per minute when exercising. He looked down at her worn Birkenstocks and said, "Your shoes will have to change."

The doctor cranked up her oxygen and told her that if she wanted to get a transplant, she'd need to be able to do 15 sits-to-stands in a minute. He said this was non-negotiable. She won't be able to use her arms after the surgery to get up from a chair or bed, he explained.

He asked her to climb off the exam table and show him some squats.

Claire -- who used to do yoga six days a week, loved to swim and even went through a phase when she did difficult workout videos like P90X with her dad -- crossed her arms in front of her chest and showed the doctor all she had.

For the first time that day, her cheeks had color.

"I don't anticipate you'd be on the list for too long," Afshar blurted out.

Given her blood type and her condition, he said, she'd probably get a transplant within three months of being approved -- if she's approved.

The first full day of evaluation appoitnments complete, Claire and her mom breathe sighs of overwhelmed relief.

Claire's eyes opened wide, and her mom appeared to melt into her chair. Suddenly, it seemed real.

"Three months!" Yeager said outside the center. "That made me want to throw up a little bit."

"I'm a little overwhelmed," Claire said. "I need to go back to the hotel and binge-watch 'Real Housewives.' I want to see white women fight over nothingness."

Hoping for a chance

The truth is, according to Claire, not longing for different lungs for most of her life served her well.

She was able to "work with what I had in front of me," she said, rather than fixate on what she didn't have. She also suppressed that part of herself that might have simply dreamed of something more.

"If I had told myself things could be better than they are now, I think I would have driven myself crazy with frustration and jealousy over other people's lives," she said.

In changing her mind, she said she had to swallow some of her pride and "open this floodgate of emotion that I kept really deeply buried."

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A slew of tests still awaited Claire, but she was now all in. She had opened herself up to the possibility that life -- for her -- could be different and not as challenging.

"For the first time ever, I'm going there, and it's really scary," she said. "Now that I actually want something better, what if it doesn't happen? What if I don't get it? What if it goes wrong?"

The pressure is on, and Claire can only hope that she will be given her chance.