Sarah, from Thornhill, has been living at Toronto's Sick Children's Hospital since last October, almost since the time she was diagnosed with a rare form of leukemia called acute myeloid leukemia, or AML.
Her mother, Leah, left her job and even shaved off her long locks to match Sarah's.
Her father, Mark, took a leave of absence from his work to be by her side, renting an apartment next to the hospital.
Sarah has had more than 50 blood transfusions in the last few months.
Family and friends even held a blood donor clinic in her honour.
Sarah's leukemia is in remission now after the latest round of chemotherapy. But if there is a relapse then a bone marrow transplant may be the only option.
Her family members are not a match — and the national bone marrow registry hasn't turned up a match either.
"The better the match the less, or smaller, the chances of transplant-related problems or mortality," said Dr. Maarten Egeler.
The Watkins have started a Facebook page called Sarah's Drive for Hope. They want to raise awareness and get more people to become bone marrow donors.
They point out that becoming a bone marrow donor is easier than donating blood. There are no needles involved: all that's required is taking a swab of your cheek and mailing it in.
The bone marrow transplant, if it happens, is a relatively routine procedure.
The after-effects are a tenderness and bruising around the hip. Some people say it's similar to taking a tumble on the ice — it leaves you a little sore for a day or two.
A bone marrow drive for Sarah will be held on Feb. 12.
Her mother says she hopes it works, "but if we can find a match for somebody else, I feel it's all worth it."