I have to say that when it comes to gluten, if she is 'sensitive', then a little can be doing a LOT of damage. If she responded to a gluten-free diet, then that is what really may be needed. It is not easy, but being consistent makes all the difference. Don't take her sensitivity too lightly. If you have not already, please google a site on celiac and children. Read some of the symptoms and see how much matches your daughter. If she is intolerant, it is critical that you get her on a strict gluten-free diet as soon as you can.
Also, for her digestion, make sure that she is drinking enough water. I know for adults it is recommended that we drink in ounces, 1/2 our weight in pounds. For a child, she may need a bit more than half her weight. But dehydration can really affect digestion. When my daughter gets a stomachache after eating, I have her drink some water, and it oftens helps right away. Then I try to have her increase her water intake in general.