Both of my children do not eat gluten, dairy, or soy. (Just my disclaimer, so you know where I stand on gluten!)
There is no WAY I would stop giving a child gluten on the say-so of a physical therapist. I do know that gluten can be inflammatory. Does your child have another issue, besides a birthmark? Why is she receiving PT?
But please ... talk to a physician about that. While no one specifically needs gluten, once you remove it, your diet can become very restrictive and the diet is difficult to follow (especially for children).
Again, just so you know ... the last time my youngest (almost 8 years old now) had a morsel of gluten (one small bite of a curly fry, the kind with seasoning on it) he missed two days of school and had a seizure. It is no small matter in our house. But we saw a pediatric gastroenterologist and got a scope and biopsies. We got allergy tests. We worked with a special needs dietician.
So, it may very well be that a dietary change could help, but
investigate, investigate, investigate.