Diabetic Girl and Yellow Lab Bond While He Works to Keep Her Alive

— -- Coach may look like an ordinary dog, but the yellow Labrador retriever is anything but. He’s Elle Shaheen's guardian angel.

Coach works 24 hours every day to keep the 15-year-old Portsmouth, New Hampshire, girl alive.

Elle has Type 1 diabetes. If her blood sugar is too low, she could have a seizure. If it’s too high, she could sustain serious, permanent damage.

Elle’s parents say they first noticed a change in their daughter about seven years ago.

“She was very irritable at times for no real reason,” her mother, Stefany Shaheen, told ABC News in an interview on Tuesday. "We couldn't really explain it. She was having trouble in her math class, which happened to fall after breakfast. And then, right before her diagnosis, she was clearly really sick."

Added Craig Welch, Stefany Shaheen's husband and Elle’s father: "Any parent who experiences that wants to trade places with (their child)."

Elle, a granddaughter of U.S. Sen. Jeanne Shaheen, said she had to test her blood sugar between 10 and 12 times every day.

"And I had to take insulin shots every time I ate, every time my blood sugar was high, and every time before I went to bed," she said.

Elle had to be monitored continuously. Then, her family learned about diabetes alert dogs, which can smell changes in blood sugar and signal immediately.

It takes at least 2,000 hours to train a service dog, according to Sarah Holbert, the CEO of Cares, Inc., a Kansas organization that provides assistance dogs to people across the country.

"We're doing scent training, 'Can you find this?' 'Can you find this toy?' 'Can you find this ball?' 'Can you problem solve?'" Holbert, who is also a dog trainer, said of the work that goes into training a service dog.

Elle's family was on a waiting list for two years to get a diabetes alert dog. When she finally met Coach, it was love at first sight.

"The immediate feeling of relief came over me," Elle said. "Especially the first time he alerted me, just knowing that he was actually going to work."

Even during the interview with ABC News, the 4-year-old dog alerted Elle to an increase in her blood sugar. She did an immediate test and found that her blood sugar level was 339.

"If Coach wasn't here, I probably wouldn't have tested, and I would've sort of blown it off," Elle said. "And then I probably would've waited another hour or so to test my blood sugar and I would've been so much higher."

Welch said Coach has taught the family "that you can find hope and you can find light in unlikely places."

Elle agrees.

"I don't know where I would be without him," she said.

The family has had Coach for more than two years.

Stefany Shaheen watches her daughter and Coach make their way through the world together, saying their bond gives her a sense of relief.

Shaheen has written a book about her daughter and her dog. "Elle & Coach, Diabetes, the Fight for My Daughter’s Life, and the Dog Who Changed Everything," will be released Tuesday.