I don't want to scare you, but, I felt the same way when my X was doing this same scenario with my then 12 yr old daughter. I thought there is no way he can claim anything other than I am a good mother. WRONG! He has lied, lied, lied, making false abuse allegations against me and my now husband. He tried to coax my daughter into backing him and she did somewhat, but not to the extent he was pushing for. He tried his best to alienate her by telling her lies about me and bribing her with how great things would be at his house. He had my DD run away 2 X. He was trying to show the court that she is so miserable with me that it would just be safer for her to live with him etc....Do not get all cozy thinking he won't attempt this. He can and he might. Of course he does have to prove his allegations, but in the meantime you have to live with the accusations, possible CPS investigations and open your life up to scrutiny like no other.
My X played the same pity game with DD. I love you more, you are my only child, your mom has your brothers. Your step dad doesn't love you and can't love you like he does his own kids. Never mind her step dad has raised her since she was 18 mos. old, he is the one who read to her at night, coaches her teams, financially supports her etc...X is a loser who lives life as one big party, hasn't worked in 7 yrs. See's DD when he has nothing better to do, it goes on and on.
Do as other posters said, get DD into counseling NOW! I didn't see any of this coming until it was almost in full swing. Be proactive and cover your bases now. You may be a great mom and provide a wonderful home for your daughter, but the court doesn't know this and he may very well conjure up some nasty stuff to suit his own ends.
Good luck to you!