A: Hopefully, there's a more common explanation. Little girls often develop sensitive, irritated skin in their delicate parts, and pee and poop can make the area burn. See her pediatrician quickly because little irritations can turn into urinary tract infections if left untreated.
While I can't speculate about whether your child has been abused, I can say this: Children who are being abused tend to show multiple symptoms, including changes in behavior, mood, sleep, appetite, and energy level over more than a couple of weeks. If you're concerned, do an in-depth check of her daycare situation -- review their licensing, show up unannounced at unusual times to observe, check in with teachers, and ask other parents for their opinions. If you're not reassured, report your findings to your daughter's pediatrician, as well as any daycare licensing board, and change daycares immediately.