When your daughter complains about stomach aches, put your ear to her stomach and listen. You know what your stomach feels like and sounds like when it hurts. See if you can find any "noises" in her stomach like yours. Also listen to her stomach when she doesn't complain of pain to see if there is a difference.
See a doctor to run a food panel (they will have to draw blood) for allergies. Have the doctor test for parasites. H. Pilori (sp?) can be found in tap water and will be detected through a stool sample (May have to have a couple of stool samples taken). The stool sample may also show if there is blood in the stool.
Keep a food log/diary all the time and list her condition/mood, such as lethargic, cranky, etc. Maybe there is a link between what she eats and her belly aches/crankyness/etc. Take both the food log & if you notice 'belly sounds' to the doctor.
I have a daugter with digestive problems and we regularly see a Pediatric Gastroenterologist. I believe my daughter's dietary/digestive problems are due to her prematurity.
Bottom line...bring your girl to a doctor.