give up on the whole milk for a while (until the diarrhea clears) and then start back on lactose-free milk (lactaid) to see what happens. keep in mind that there are many things that can cause loose stools in children so don't automatically blame the whole milk but lactose intolerance is a possibility. can she eat yogurt cheese or even ice cream?
my one year old gets diarrhea after having whole milk is she lactose intloerant. we started our daughter on whole milk two weeks ago and about a week later she started having very runny stool and diarrhea. when she was a infant we had to change her formula to gentle ease because of the same problem. so not sure what we should give her or if she is lactose intolerant her doctor said she should not be still because most infants don't have the same problem when they get older but she still does