I agree that this could be a diet-related condition, and it could even be a signal that your daughter has food allergies or sensitivities.
Wheat, dairy, and sugar all feed yeast, which kills off the friendly bacteria in the body. It's a good idea to avoid all three. Wheat and dairy are two of the most common food allergies and sensitivities.
Wheat compounds allergic reactions, even to other allergens. Dairy contributes to chronic pain and to break-outs. Sugar is feeds yeast and should be replaced with honey or real maple syrup.
Try avoiding all three foods for two weeks to see if her condition improves. My doctor switched me to this diet a year and a half ago, and my health has improved dramatically. It's easier to follow than it seems at first, and the changes in my hair, skin and nails is amazing. If you're interested in a full outline of the plan and some meal ideas and restaurant ordering suggestions, send me a private message and I will send it to you.