Okay, you've got some great advice here. I would agree that the first thing to do is look at diet and food sensitivities. Our food supply is terribly contaminated with foods that are no longer digestible. GMOs, too much hybridizing, chemicals, etc make things that were normally staples in the human diet (wheat for instance), intolerable.
Eliminate wheat (and gluten containing foods--see celiac's website), sugar, corn syrup, dairy, nightshade vegetables (tomatoes, potatoes, eggplant) and red meat right away. Stay off of them for two weeks. The whole family should get on the game with her for this short term. It will be easier, and Others in your family may have some sensitivity also that will only become obvious when the irritants are gone. Stick to whole foods (the less processed the better, so brown rice instead of white, whole fruit instead of juice). Eat lots of green veggies, fish, organic chicken.
Get some flax and borage oil into her diet, if you can, by mixing it with other foods (I use it in salad dressings). Get ahold of diatomacious earth (food grade) and get her to take it mixed in water or a little juice. This will clear parasites, yeast, and other internal beasties from her system.
Lots of water, water, water. Purified or at least filtered if possible.
This is a detoxifying diet. It is gentle, though sometimes seems radical because the changes can seem enormous to take on. Just try it for two weeks. It will eliminate irritants, clean out the system, and allow the intestines a chance to PROPERLY absorb nutrients.
After the two weeks, reintroduce ONE category at a time, for just two days (bread, nightshade, dairy). Probably best to avoid sugar and corn syrups for the long haul. These are hightly processed foods that should be enjoyed only on a very infrequent basis. You will notice how these foods affect her when you reintroduce them in SMALL QUANTITIES. After you introduce one, take a day or two to let her clear out again without it and see the difference.
I know this is a lot, but it will give you some real answers, and you are in control of it. In the long run, this is cheaper and less time consuming than doctors and crazy medications. Also, if she is celiac or has crohns, you will know it from eliminating the wheat and you will save her intestines from further, sometimes irreparable, damage.
Good luck! I had to do this for myself and it is AMAZING what you can learn about yourself/your child by trying this method.
Best,
S.