I can speak to both sides of this (not medically, just personally). My 11 yo daughter will NOT pull out loose teeth, they hang by a thread and just fall out months after they are loose. So in almost every case, the adult tooth has been WAY in before the baby falls out. They've never had to pull anything. But hers came in more straight underneath, not behind (which I think is what you are describing). My sister's daughter, 5 years old, did have to have a tooth pulled (can't remember the exact circumstances). My sister was nervous, but it turned out to be no big deal at all. They didn't let parents go back with the kids (which I don't like) but even that was fine. I think if you need to prepare her for anything, it is probably the possibility of a shot of novacane and perhaps that you can't be with her the whole time. She shouldn't be in any pain. Good luck.