gluten is part of protein in wheat (but sounds like she doesn't have gliaden allergy--the other half of the protein in wheat??) and casein is the protein in dairy...am not positive what protein she would be allergic to in oats.
I will dig out the website that has all the commonalities of allergens if I can find it. It sounds like corn is OK. Rice is always the least allergenic...what about rye? or kamut or spelt?
They now make corn elbow noodles; you can use corn tortillas. Several breads are now made with rice (though I think they taste horrid)...be careful with any soy cheeses as many of them actually ADD casein to their product. Soy milks and soy yogurts would be safe to use.
You said she was small; children can often outgrow food allergies, but proteins are difficult...best of luck
Thoreau said, 'A man is rich in proportion to the things he can leave alone.'