E.B.
I understand the recommendations for eliminating gluten and dairy, but I'd like to offer a suggestion. Don't eliminate both all at once at the same time. Eliminate one at a time, and give the trial about 2 months before you evaluate the effectiveness. That way, you will know which elimination gave your child the most benefit. Since she doesn't have Celiac disease or a true dairy allergy, you have no way of knowing if eliminating one or the other or both will help her.
My daughter has many medical problems, and at different times doctors have had us try eliminating gluten, corn, dairy, etc.
Many gluten free products are marketed to replace the identical glutenous product. For example, "English muffins". They slightly resemble regular English muffins, except that they can contain far more ingredients, and extra sugars and fats. The same can be said for many breads, pancakes, and cookies. Sure, you'll be eliminating gluten, but adding in preservatives, sugars and fats. So read labels carefully. Some delicious options include pretzels. The gluten free pretzels are indistinguishable from regular pretzels.
Don't load up on a grocery cart full of gluten free products. Try one. You might find it very acceptable or you might think it's just awful.
And learn which products contain surprise gluten (soy sauce, Worcestershire sauce, some salad dressings, bags of shredded cheese).
Kids usually like rice. There are some good gluten free snacks. Instead of a peanut butter sandwich, spread peanut butter on apple wedges. There are some great breakfast cereals that are now gluten free. Lundberg brand brown rice pasta is delicious. We preferred rice pasta over corn pasta.
When you try dairy free, Earth Balance and Smart Balance make delicious dairy free options, and they are much better than margarine. Rice milk is good on a bowl of cereal (the cereal usually gives the rice milk some good flavor). A lot of the almond and soy milks contain carrageenan and other additives. It's pretty simple to make your own milks. Oat milk is delicious and tastes like oatmeal. There are plenty of recipes for making homemade milks online. Oats are also quite cheap - making almond milk can get pricey.
Most of all, don't go at it from a negative perspective. Don't say "you can never have bread again". Instead, think of it as supplying the body with good fighting soldiers or as putting good things in to feel healthy. Try not to serve the whole family a bread based meal (sandwiches, spaghetti with garlic bread) and serve your daughter a poor imitation. Instead, try to include your daughter. Don't make a huge deal of it. Just serve rice pasta with a good homemade meat sauce to everyone. Use rice and make a stir fry. There are lots of corn chips and tortillas that contain no gluten, so you can make tacos or nachos. Think of this as making your daughter as healthy as she can be. And be strict. Don't do this half-way.