Tehachapi, California (CNN) A new engagement ring adorns her finger, and fresh congratulatory balloons float in the room. But in Rachel Sheppard's hand is a reminder of the horror that also hangs in the air. It's the bullet that was cut out of her back two days earlier -- one of three that tore into her body last fall in Las Vegas.

"Seeing it in person, it all still seems so surreal," says Sheppard, 26, while seated at her dining room table a few weeks ago. "This crazy, insane massacre happened. I think about it every single day."

Sheppard was one of more than 500 people injured when a gunman opened fire on the Route 91 Harvest country music festival in October. Another 58 people died. That she survived, especially since one bullet ripped into her aorta, is astonishing. That she was home less than a month later and is walking around and able to talk about it is mind-blowing -- not least of all to her.

"They said I was one of the worst critical patients," she says of the staff at Sunrise Hospital and Medical Center in Las Vegas, where she arrived by ambulance. "Nobody thought I was going to make it."

Somehow, she did. And while she's looking ahead and already planning her wedding, Sheppard is still coming to terms with how her life changed in an instant. So are two people who journeyed with her that night.

Into the unknown

A blown-up photograph, taken at the festival just hours before the shooting, is taped to the wall by her Christmas tree. In it, Sheppard smiles widely, her arm flung around a friend in a floppy-brimmed hat. She sports sunglasses and the sleeveless burgundy top that will later be soaked in blood and cut off.

Not too far away in the crowd of 22,000 concertgoers, Jake Codemo would soon split with his two "guy trip" buddies. They wanted to grab something to eat; he insisted on staying for Jason Aldean's performance. "Come back and find me," Codemo, 30, told them.

With the first barrage of gunfire, Codemo didn't know what was happening. The second burst made it clear, and he turned to run. He hadn't gotten far when he stopped short, his eyes having caught a stranger's. Alaina Kelly stood over Sheppard's body, screaming for help.

Kelly, 23, had only met Sheppard two days earlier, even though they both live in the area of Tehachapi, California. Kelly came to the three-day festival with her parents, her siblings, a friend and their significant others. Her brother's girlfriend invited a friend, Sheppard, to join just a week before, when the group realized they had an extra ticket.

The "kids" hung out all that Sunday at their hotel pool and then at the festival.

Just hours before the shooting, Rachel Sheppard, third from left, and Alaina Kelly, center in white, enjoyed the festival with thousands of other country music fans.

"I had been drinking a lot that day," Kelly says. But she remembers the first round of gunshots and then finding herself frozen after her group scattered, unharmed, and she was left behind with Sheppard.

Codemo says he never had time to think. He grabbed Sheppard under her arms, an unidentified man took her feet, and they began to run. Kelly raced alongside them. She watched as Sheppard's arms flailed about, and she held hers above her own head, hoping to protect herself from gunshots.

With another burst of fire, they all fell to the ground to take cover. The unidentified man turned his attention to a new victim, and somehow Codemo -- with or without Kelly's help, no one is sure -- darted off with Sheppard into the unknown.

"To this day, I don't know where the medical tent was," Codemo says. "We just happened to run directly to it."

The relief of making it to the tent was tempered by what followed.

'Like sitting ducks'

Nearly 6,000 miles away, Sheppard's boyfriend of more than four years, Jesse Morrow, woke in a Milan, Italy, hotel room. He'd arrived just hours earlier for work. The drill rig mechanic got a call from a friend who'd heard the news from Sheppard's friend -- the one who'd invited her to the festival.

"There was a terrorist attack," Morrow, 28, remembers his friend saying. "Rachel was one of the ones that got hit."

He'd flown to Italy the day before, with plans to propose after he returned. Now, he was frantic to reach the woman he longed to marry. Using the mobile application WhatsApp, Morrow says, he must have called her 25 times with no luck.

She was in the medical tent where only a few people were qualified to offer help, says Codemo, who'd carried her there. The ongoing gunfire left everyone in the tent out of reach of ambulances and, he says, stranded "like sitting ducks." A man who stood by a wounded loved one inside the tent took a bullet in his back, right next to Kelly.

The tent grew hectic with screams and filled with victims and others trying to help. Some who'd been shot had people with them. Others lay bleeding alone. Some had "parts blown off," Codemo recalls. A woman lay nearby, her leg "split off at the hip."

Kelly looked around and grew hysterical. Codemo was determined to rein her in.

"Focus on Rachel!" Kelly remembers him screaming."Stay here!"

Rachel Sheppard says she and Jesse Morrow knew they would marry, but the Vegas shooting "solidified that this person would be my forever."

Someone shoved an IV in Sheppard's arm, and Kelly held the bag. After Sheppard's top was cut off, Codemo removed his own shirt, using it to apply pressure to her wounds. He says he used his fingers to try to stop the blood that kept pooling beneath her left breast.

Sheppard, still awake, thought of her boyfriend. Kelly had Sheppard's purse and was asked to pull out her phone and call Morrow.

"Are you OK?" Sheppard remembers him asking.

"I don't know," she told him.

"I called him because I didn't think I was going to make it," Sheppard says. "We just kept telling each other we loved each other."

Morrow hung up and rushed to the airport for the first flight he could get.

'It's all in your head'

When an ambulance pulled up near the medical tent, Codemo and Kelly rushed Sheppard toward it. It was full, but Codemo pleaded to get on board.

"If I hold her, can we go?" he begged. "She's lost a ton of blood. ... I don't think she's got much left."

He held her on his lap in a corner of the ambulance, hiding her face so she wouldn't see the man in front of them with a gunshot wound to his head. Kelly reached out to hold the man's hand. He was dying, and she didn't want him to feel alone.

Sheppard's breathing grew shorter, and she complained about the pain.

"I had no clue how she was alive," Codemo said. "It was confusing how she was still talking."

Sheppard credits lessons from her parents for keeping her present. As she struggled, she focused on her breath to try to stay calm.

"Deep breath in. Deep breath out. Through the nose, and out the mouth," she told herself.

Jake Codemo, center, with his friends less than an hour before the shooting. They had a room at Mandalay Bay, two floors beneath the gunman.

"Growing up, my dad and my mom always taught us it's all in your head," Sheppard says. "If you mentally shut down, your body will do the same."

Codemo could shield her face for only so long. Once they got to the hospital, there was no hiding the gruesome chaos. Victims in wheelchairs lined the hallways. Blood covered the floors and walls, Sheppard remembers. She cried and yelled in pain, "I can't do this!" She began to vomit blood.

The last thing she remembers before being put under was a man grabbing her face and looking her in the eyes.

"You're going to f***ing make it," he told her. "You're going to f***ing do this."

She has no idea who the man was.

Five gallons of blood

More than 240 patients poured into Sunrise Hospital's trauma center the night of October 1.

Sheppard's "injuries were very critical and of those treated as part of the (mass casualty incident), she was clearly one of the most challenging," Dr. Jeffrey Murawsky, the hospital's chief medical officer, said in a written statement to CNN.

The tear to her aorta -- the main artery that carries blood from the heart to the rest of the body -- ran from her upper to lower abdomen and affected the blood flow for her kidneys, Murawsky explained. The surgical repair required quick precision, grafts and complicated attachments. Her liver too was torn by a bullet. And she sustained injuries to her intestines and abdominal muscles, as well as a fractured vertebra in her lower spine.

"Rachel required many units of blood and blood products and multiple surgeries to correct her injuries," Murawsky said. "They were initially severe enough to even cause her to require CPR to maintain her blood flow."

She heard that she received 40 units -- "a five-gallon bucket," she says -- of blood. A red scar runs from above her sternum, where doctors cracked open her chest, down to her pelvic bone.

For three days, her abdomen was left open so doctors could evaluate her healing, Murawsky said. Her body swelled as she lay in the ICU.

Rachel Sheppard's scar serves as a constant reminder of how close she came dying in October.

"She looked like a baked potato," split down the middle, says Morrow, her fiancée, who rushed back from Italy to be by her side. "She was swollen so bad, her fingers looked like rolls of quarters."

Doctors predicted that she'd be in the hospital for three to six months, but she was out in 18 days. After six days in a Bakersfield, California, rehab facility, about 45 minutes northwest of where she lives, she went home.

Today, her fingers clutch the handles of an exercise machine at physical therapy, where she goes three times a week. She lost 30 pounds in the aftermath of the shooting and, with months of limited mobility, is working to strengthen her core, upper body and balance.

An X-ray picture she pulls up on her phone illustrates some of the toll on her body. Wires, crisscrossed like shoelaces, hold her sternum together. A bullet, since removed, rests near her fractured lower vertebra. Her spine now exhibits slight scoliosis, curving to favor her left side, where she took the shots.

She emerged with a dropped right foot and a right big toe that turned "floppy," sometimes dragging and causing her to trip, she says. Using electrical stimulation and resistance bands, physical therapists are working to re-educate her muscles.

She also is still grappling with numbness and tingling sensations in her legs. The discomfort makes heavy blankets, even some clothing, unbearable. She and Morrow are relearning how to cuddle.

Other people receiving physical therapy look over at her in awe.

"This woman is amazing. I was in Vietnam, and I saw a lot of this stuff," a man getting rehab after shoulder surgery says of her injuries. "The men, of course they were boys, they would have laid there and given up."

'Why did I live?'

Determined and upbeat, strong and stoic -- that's the face she wears at therapy and most of the time. But back home, Sheppard allows herself to feel, even though she says she's all cried out.

She can't help but struggle with some survivor's guilt, and the tears fall as she explains.

"Why did I live?" she asks. "Why won't I have more injuries for the rest of my life compared to someone who was shot once? Why am I walking and others aren't?"

Once fiercely independent, she's now terrified to be alone. Loud sounds make her jump. She scrutinizes strangers in a new way. She's also angry that she and others at the festival don't know how the mass shooting happened. She is among the many who've filed lawsuits in a desperate search for answers.

She thinks about it every day and would like to see a qualified therapist, a trauma specialist. But finding the right person to talk to in her small community -- and one who will be covered by her limited medical insurance -- hasn't worked out.

Sheppard is changed, she knows that, and so are Kelly and Codemo, the two people who were with her that horrific night. What they shared connected them forever, they say, and the three remain in close touch.

Alaina Kelly and Jake Codemo visit Rachel Sheppard for the first time after the night of the shooting at a rehab facility in Bakersfield, California.

Kelly panics in large crowds and can't listen to loud music. The sound of a passing ambulance days after the shooting sent her to the side of the road in a panic. Nightmares haunted her for a while, and she ended up dropping her college classes.

But Kelly also learned about herself. She has a new understanding of what she's capable of and plans to resume classes with the aim of becoming a nurse.

"I'm a fighter and not a flighter," she says. "I definitely don't want to waste my life. I want to experience everything I can, but that's also hard because I'm scared and nervous to go to new places."

Then there's Codemo, whose contact information is saved on Sheppard's phone under the name "Jake (saved My Ass)."

Codemo, a journeyman lineman who works on electrical power lines, got home to Ventura, California, where he hugged his wife and three young daughters extra tight.

"Every day, it makes me think about life a little differently," he says of what he experienced in Las Vegas.

He lost his own father when he was pretty young and doesn't want to take anything for granted. Nor does he want to live with regrets, which is why he is now on an epic three-week trip with his wife.

They just finished hiking to the top of Mount Kilimanjaro in Tanzania, he said in a text message Monday. Next up, they are heading to the southern end of the Serengeti National Park to witness the Great Migration of wildebeest and zebra. After that, they're off to Zanzibar to scuba dive in the Indian Ocean.

"I've always been a guy who lives life in the moment," Codemo says. Now, he knows there is simply no better way.

Cheering her on

Before the shooting, Sheppard was a longtime bartender and server who hoped to build a wedding and event coordinator business. Doctors have told her it'll probably be a year before she can get back to the local Mexican restaurant, where she lifted kegs and 30-pound trays.

The walls in a corner of her living room are covered in messages from those cheering her on. There are cards from children in Las Vegas, red hearts filled with well wishes collected from a nearby fundraiser and a big poster board crowded with notes from co-workers and customers at the restaurant.

"We are all missing you like crazy around here. ... I can't wait to see you soon behind the bar singing 'Pina Colada,' " one woman said. "You are the most amazing bad ass I've ever met. I cannot wait for you to see how many people have loved and prayed for you," another wrote. "May God bless you & continue to make you stronger," said a third, ending the message with "#margaritastrong."

Taped to the large poster board is a letter written by a nurse who tended to her at the very beginning.

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"I will never in my life forget you. You -- my sweet patient Rachel -- are still supposed to be on this planet," she wrote. "Take that and run. Never look back. Enjoy every second. ... Accomplish the job God has kept you here for and have a blast doing it."

Sheppard is not a religious person and can't say she necessarily believes in God. But she does believe that "things happen for a reason" and that some force was on her side that night in Vegas. She believes the prayers of others mattered.

Where all of this will take her, she doesn't know. She doesn't want to have to know. She doesn't want to promise that she'll be a leader in any sort of movement or take on the pressure to live an extraordinary, uber-accomplished life.

"People want know, 'What are you going to do now?' " she says. "I just want to do me and, at this point, focus on my healing."

She wants to breathe in, breathe out and be present.