Thats so sad that her dad is trying to force his name on her. I had my biological fathers surname till i was 10 and my mum re-married. He had to sign a court order thingo to say he aggreed to the change, which he did, but wasnt too happy about it, but i wanted the same last name as my mum and family.
It made a big difference to me that my name was the same as my mums, hugs to your DD, hope your ex wakes up to himself soon and realises hes being a bit of a ......