As a child, her struggle was hidden behind a beaming smile; her main source of joy was riding her pony. And it was a brave smile, the same one that greeted doctor after doctor, even in the face of constant pain that Hughes lived with since she was a baby.

Sarah was diagnosed with systemic juvenile idiopathic arthritis when she was 11 months old, her mother, Fiona, said. It's a debilitating autoimmune disease that affects multiple organs and systems in the body and impacts 30,000 children in the United States, according to Dr. Jeremy Szeto, a member of Hughes' medical team.

Hughes' aunt -- her mother's twin, Sarah Jane -- passed away at 37 after her own struggle with juvenile arthritis. It was days before Sarah's seventh birthday. After losing her beloved aunt, it was years before Sarah wanted to celebrate the day.

It also reminded the family what doctors had said about the eventuality of Sarah's condition: It was a death sentence. But the mother and daughter were determined to fight the disease and strive for normalcy.

Growing up in the hospital

Months after Fiona gave birth to Sarah, little pockets of fluid began to appear around Sarah's joints, and she suffered from fevers that reached 107 degrees. When Sarah began to crawl, she moved awkwardly to avoid using her painful, swollen joints.

After visits to a succession of doctors and blood work that tested positive for autoimmune disease, Sarah was put on low-dose medications. She was fitted with little braces so that her joints weren't deformed. Fiona focused on trying to keep Sarah's life as normal as possible. At 18 months old, she was sitting on a horse, sharing in one of her mother's passions.

But at 4, Sarah began to have migraine headaches that left her screaming on the floor. Fiona panicked, especially when she saw Sarah tilting her head to the side. Doctors discovered that Sarah had arthritis in vertebrae just underneath the base of her skull.

"It was the first time I was told that her life was in jeopardy," Fiona said.

The arthritis was growing and spreading through Sarah's spinal cord and affecting her heart and lungs. To protect her vertebrae, Sarah was put on TNF blockers, a type of medication that suppresses the inflammatory response.

Soon, the rest of her body was under attack. Her digestive system shut down, and she developed antibodies that turned against her immune system. Sarah's symptoms would only grow and worsen as she aged.

Challenges mounted for Sarah when she went to elementary school. She had to navigate the hallways on crutches while someone else carried her backpack. Aggressive treatments and medications caused her hair to fall out. She couldn't eat and was tube-fed through her stomach or an IV, which made Sarah feel nauseous.

Sarah wanted to make friends so badly that she didn't tell Fiona about the bullying she faced. No matter how hot it was in Houston, she remembers wearing a thick, navy cardigan over her dress to keep other girls from pulling her dress' zipper down. They thought it was funny how her hair would catch it and fall out.

It wasn't long before Sarah would be considered a "homebound" learner, using the aid of teachers who would visit her at home or drop off assignments for her to complete.

'A club you don't want to be in'

Although the TNF alpha blockers had protected the top of Sarah's vertebrae, her digestion issues worsened and soon the rest of her spinal cord was plagued by antibodies, causing holes to form along her spine. Sarah was also allergic to many of the medications she took, creating new symptoms such as hives and other allergic reactions.

This domino effect led doctors to tell Fiona that Sarah's body wouldn't be able to sustain itself; the IV nutrition would destroy her liver and gastric feeding tubes were not sustaining her weight. She was still elementary school age when they gave Fiona a talk about how to keep Sarah comfortable for the rest of her life, however long or short it might be.

"I called the specialists together and said 'I know you can't fix her, but I'm mad at you for giving up on her,' " Fiona said.

Fiona didn't give up.

Sarah's doctors arranged for Sarah to be evaluated and treated at the National Institutes of Health in Maryland, where she underwent extensive testing. Her type of juvenile arthritis was so rare, doctors there referred to it as "Sarah's disease." Even if there wasn't much they could do for her, researchers were able to learn more about the disease over years of working with Sarah, and she knew it could help them to treat others.

By the time Sarah was high school age, she looked like a cancer patient, she said. Between her aggressive disease, her 23 maintenance medications and routine chemotherapy treatments, she had bald patches on her head and dark circles under her eyes. Her weight dropped to 83 pounds.

Sarah's medical team predicted that she would die in her early 20s. As her body wasted away, Sarah spent most of her time flat in bed with no energy and in constant pain. A small trip outside of the house would take three weeks of recovery time.

The illness caused her to graduate from high school three years late, but Sarah was determined to walk across the stage to receive her diploma, even though she could barely walk. The students in front of and behind her helped to push and catch her as she moved across the stage.

The one bright spot was Tucker Beau Hyatt. Fiona first met Tucker Beau's mother, Linsey, in 2011. As mothers of young patients with such a rare form of severe arthritis living in Texas, they hoped that their children could be friends. The two bonded instantly and their personalities just clicked, even though Tucker Beau was only 5 and Sarah was 21. They had honest talks about their disease, wore matching Batman shirts for strength and constantly talked on the phone or in person. As her condition deteriorated, Tucker Beau would call often to make sure that she was still alive.

"This kind of pain and loneliness is like being in a club you don't want to be in," Sarah said. "I became a sister to him."

One last option

When she was 22, Sarah learned about stem cell therapy offered by Dr. Stanley Jones, the co-founder of Houston-based Celltex Therapeutics, which specializes in stem cell banking and therapy.

None of her other treatments was working, and her body would reject donor cells. But the hope was that stem cell therapy could duplicate her own healthy stem cells and infuse her body with them. Because stem cells can rebuild and regenerate in areas of destruction, infusion treatments could possibly help Sarah's body to repair itself and regulate her overactive immune system.

For months, Sarah and Fiona researched this type of treatment. Her condition continued to deteriorate, and Sarah wouldn't have time to wade through the bureaucratic red tape surrounding what the U.S. Food and Drug Administration would allow if she wanted the treatment to happen in her home state of Texas. To receive the procedure without delay, it would involve a trip to Mexico.

They were especially encouraged after Tucker Beau had the treatment and responded well. Shortly after her 23rd birthday, Sarah decided to pursue stem cell therapy.

"I realized at the time that the life I have is not living, it's not a life at all. I just want to try," Sarah said. "I had watched my aunt die from this and saw what could happen. I always knew that could happen to me, I just didn't know when."

Fiona and Sarah made the trip to Mexico, along with Tucker Beau and his mother so that the friends could be treated together.

Within two hours of an infusion, Sarah could feel changes in her body. She felt a little burst of energy that empowered her to talk, sit up and start walking with aid. But even more surprising was that Sarah was hungry and wanted to eat, a sensation she didn't recognize after a life of being fed through a tube or or intravenously.

Two months after the treatment, Sarah's digestive system began to normalize. Finally, she could eat food for the first time without the use of a tube. Like a child, she would look at menus and ask her mother what she might like.

Sarah's hives and infections have disappeared, her joints are no longer inflamed, spinal leakage has stopped and her once-inflamed eyes are clear.

A year after her first stem cell treatment, Sarah has stopped her chemotherapy treatments and cut out almost all of her maintenance drugs. She has received several cycles of therapy, totaling 2.5 billion of her own stem cells since the initial treatment, and she will receive more in 2016. Her physicians will reevaluate Sarah in 2017 to see whether her immune system has learned to self-regulate after two years of stem cell therapy.

"I have hope now, and I didn't have that before," Sarah said. "My life is 100% different."

A new lease on life

Sarah is adding to her college course load through a community college so she can graduate sooner, riding her horse Stirling Bridge, swimming, starting to drive and learning the nuances of social interaction. Up until now, Sarah's entire life has been rooted in medical knowledge. Fiona is eager to see Sarah make friends, start dating and make up for all of the experiences she missed out on.

Tucker Beau, 7, is the healthiest he's been and has joined the local lacrosse team, rides his bicycle every day, goes to school and plays with his brother and sister. He and Sarah expect to be lifelong friends.

Sarah was more excited to celebrate her 24th birthday than she was as a child. The doctor appointments now feel more like parties, with her medical team capturing her progress and smiles in photographs and marveling at her continued progress. She's building back her muscles and gaining weight and her hair has grown back, long and thick.

For Sarah, there are pivotal moments in the little things, like getting a touch up after dying her hair.

"When I dyed my hair, I didn't know how long I would be around and I didn't like thinking about how short my life would be," Sarah said. "I wasn't planning on touching up roots. I'm here to deal with roots! I wasn't expecting to be around that long. And now, I'm planning for the future."

For Fiona, it's like seeing the side of her daughter she always wished for: happy, hopeful and ready to seize life's opportunities.

"This is a kid I didn't know," Fiona said. "She was always spunky, but what I saw was the light coming back into her. It's been fun watching her open up. I've lived my life with a lump in my throat, fighting back tears with a brave face for so long. I'm so relieved to be me now. She's her, and I'm me. We're enjoying life together, the way it should be."