Donya McCoy says she will forever feel indebted to a man she's know most of her life but only recently became close with. A former high school classmate, Mike Thompson, responded to a mother's desperate Facebook plea for a liver donor to save her 3-year-old daughter's life and turned out to be a perfect match.McCoy says her 3-year-old daughter Kennedy is like most toddlers her age, super friendly and headstrong."She goes up to anyone; she always says to people 'Hi!' and the next thing is 'Up! Up!' because she wants people to pick her up," she told ABC.But after suffering a seizure at eight months old, it was clear that Kennedy was facing medical challenges most children never experience. Doctors performed multiple tests and could see that Kennedy's brain matter was unlike anything they had ever seen and her amino acid levels were off the charts, but they had no idea what was wrong."The doctor basically walked into the room and said, 'Your daughter is a mystery to us,'" McCoy said.That was the point at which McCoy realized she need to take matters into her own hands. She began researching doctors who might be able to shed some light onto Kennedy's condition. She was eventually to referred to a retired physician who used to work for the National Institutes of Health, Dr. Harvey Mudd.Mudd came out of retirement to take Kennedy on as a patient and within three weeks they had a diagnosis. Kennedy had S-adenosylhomocysteine hydrolase deficiency, a disease so rare that Kennedy is one of six people in the world living with the disease, according to McCoy. A mutation in her DNA causes Kennedy's body not to be able to process proteins essential to growth and development and brain function.But then in January of this year, Mudd passed away, leaving McCoy and Kennedy without a physician.It was at the Mudd's memorial service that McCoy reconnected with Dr. Kevin Strauss, the doctor who had initially referred her to Mudd. Now that Kennedy had a diagnosis, McCoy hoped he would be able to help."I think he could hear the desperation in my voice and he agreed," McCoy said.Within a month, Kennedy was under Strauss' care and he said that although it had never been done before with Kennedy's disease, a liver transplant would give her the best chance for survival.Because the source of Kennedy's condition is a genetic mutation, she would require a donor that was not a relative. Not knowing where to turn, McCoy posted a message to Facebook "So I thought, the most access I have to the most unrelated people I know is on Facebook," McCoy said.She called it "the plea of a lifetime.""I can't even believe I'm posting this, but as a mother, I have to exhaust every option possible," McCoy wrote.Despite never being close friends and having not spoken in almost two years, an old high school classmate said he was interested in donating. Mike Thompson is a firefighter in McCoy's hometown of Bethlehem, Penn."If somebody calls 911, we're there to help if they need us; it's part of our job," Thompson told ABC affiliate WPVI last month. "Me doing this is something I thought would be nice to do and as of right now everything is working out," Thompson said.It turns out he was a perfect match.McCoy says hearing the news was overwhelming."I don't feel like there's ever a way that I can thank him enough," she said. "I fell indebted to him. I feel like I want this to be something that Kennedy knows is a special gift she was given by someone so selfless. That's the only way I think I could repay him, is to teach her to be as selfless as he is."Tuesday morning, doctors at the University of Pittsburgh Medical Center removed a piece of Thompson's liver, which was then transported by ambulance across town to Children's Hospital, where a second team was ready to insert it into Kennedy.McCoy says the surgery went great and both Thompson and Kennedy are doing well. McCoy hopes that a successful transplant means that one day Kennedy will get to abandon her highly restrictive diet and enjoy more foods."After her transplant she will be able to have more proteins so we're pretty excited to see what her new favorite food becomes," McCoy said.