I change the diapers at about 9:30am before we go outside because one of my little ones is a regular pooper at that time. Then I change them again at noonish before naptime and after naptime at about 3pm. Those are the regular change times with the stinky ones extra in between or off schedule a bit. If a child is prone to a diaper rash then I ask the parents to provide a cream to be kept here with their diapers and wipes and I will gladly put it on the child. There shouldn't be any other questions or answers to this issue, it's simple enough.

The fact that the parent is blaming you for a diaper rash makes me think that you had better sit her down and talk about trust and the way you run the daycare and clear the air quickly. Is she having a problem letting her child be out of her care? Is she worried about something at daycare? Ask her point blank questions and get point blank answers and assure her that you are doing a great job and she shouldn't worry, but she should always discuss things with you.