RockRose is correct, this is a symptom of her blood sugar being too high.
cb, stomach pain is a symptom of type I diabetes. Google "diabetes in children stomach pain" and you'll find lots of medical references. I didn't read far enough to see how it's treated, but it seems like you should go in the direction that diabetes and her stomach pain are related.
Best wishes.
Does she go to pre school or day care could there be any outside issue upsetting her, has she got Diarrea any other symptoms, has she eaten anything differant than normal .If it cobntinues through today take her to your Doctor to ask for further tests .Good Luck I hope it eases soon .