It's not uncommon to have regularity problems for a period of time after a bout of diarrhea in children. Motility in the gut can be sped up with diarrhea occurring even after the apparent illness has resolved. In particular, there can be mild lactose intolerance which leads to ongoing diarrhea for several weeks due to the damage causes by the virus or bacteria that originally caused the diarrhea.

I think watchful waiting is the key in your child's case. Bland foods, avoidance of milk products, and extra fiber in the diet should help. I do suggest seeing her doctor if the symptoms remain a problem for over a week or if she starts to show other worrisome signs like blood in the stool.