C.F.
It's my guess that she did bonk it and you just didn't see it happen. Sometimes it doesn't take much. my son colided with another boy and very quickly it went dark. he was about 2 or 3. We went to the dentist and decided to do a baby root canal. It lightened up the tooth a lot and kept it in there until he lost it. Funny thing is that tooth took forever to fall out. We didn't have any other problems with it. The dentist said we could do nothing and it may or may not get infected. he also said that we could do the root canal and it still may need to come out. Anyway. It all worked out. Good luck.