My son had this for 3 weeks!! First we thought it was diaper rash (Got the best meds on the shelf for that $$), then we thought it was a yeast infection (got meds for that... $$$), then we thought it was slapped cheek disease (he had a red cheek to go with this as well as a fever), FINALLY we took him to the ped and he said that he had gotten Staff, due to wetness. (When the skin gets wet and stays wet (poop or pee) it can cause a bacterial staff or strep infection. You should take her to see the pediatrician for a prescription antibiotic ointment. )
He prescribed antibiotic ointment ($10) we also got some calomine lotion for the itch and discomfort, I added some baking soda in his bath water, and let him run around stark nekkid without diapers on whenever I know he will stay dry for a while.
TELL THE DAYCARE TEACHER TO CHANGE HER EVERY HOUR FOR A WEEK. It can be that her diaper stays wet for more than 2 hours.
good luck!