J.S.
My first thought was "too much fluoride." Many towns add fluoride to their water supplies so you're drinking the stuff. It's also added to our toothpaste. Plus you said you were at the dentist... so by any chance did the dentist give your daughter a fluoride rinse?
I would switch to a non-fluoridated toothpaste and see if that solves the problem. It might take a little time though.