He requested a hyphenation. So that is a change from her current last name. Currently she doesn't care about her last name, correct. Dad denied her at birth and didn't sign the birth certificate, so she has my last name.The child's last time is likely to be hyphenated if the parents can't manage to be adults about it. Or, depending on the judge, Dad's request may well be granted in full. A complete denial of Dad's request is unlikely.
The child certainly doesn't give a flying ferret fart about her last name.