L.M.
I was going to recommend having her tested for celiac disease but I see that has already been mentioned. Read about it online. Sometimes the first test in small children doesn't come up positive but that doesn't mean they don't have it. She should be genetically tested to really know if she is predisposed. Don't let up on the doctors. This condition is underdiagnosed! It is controllable with a gluten free diet. Lots of people are doing it and it IS possible! You will save her from lots of other health problems later.
Here's one article to get you started:
http://glutenfreeworks.com/gluten_explained.php
One more re: symptoms in kids (belly):
http://www.everydayhealth.com/publicsite/news/view.aspx?i...
Take care.