First question- how old is this child?
Second- are you just changing the child's last name despite the father?
Thirdly- Is your child familiar with her last name? Have you talked to your child about a name change?- Or maybe just after enrolled in school, dropping the end of the name?
As far as I know, you can change your child's name to Barney Rubble if you would like. No one has to be notified. You are the legal gaurdian, there for, you are allowed to make any legal changes to the child's name.
Good Luck and God Bless!