A.C.
So sorry to hear how unhappy your daughter has become. Whatever your gut tells you, do so, and listen to your daughter.
I would try to have a real heart to heart talk with her. If she doesn't want to talk, since you've already thought about it, take her to a doctor just to get an all-around physical and then that doctor may reccomend a counselor. A friend's daughter has had a counselor and has seen some improvment from it. It could be anything, who knows....I'd want to seek help.
After a doctor visit and if the doctor says it's ok, I'd see if we could do visitations on neutral ground: a day at the movies, go rollerskating or bowling or something where there would be an activity to take the pressure off but where they could talk enough for the dad to feel he's getting to know her, even one of the bigger McDonalds playlands or a nice park. What did your ex go to school for? I ask because maybe you could initiate an activity on neutral ground that would show a little insight into who he is so his daughter could know him, and he'd appreciate that activity too. (If he likes cars then I'd suggest a local race or a car show coming up, if he likes history art or science then a museum or fair, that kind of thing). Another option would be to have a casual family day with him included. That way she has the security of knowing that you're there, but could spend some time with her dad. You'd be there, maybe to assist the interaction in a non-threatening way and also to make sure all goes well. Personalities shouldn't swing so wildly, in my opinion. I'd want to be present (but act nonthreatening so that it could work).