When you get married your DD can legally take your new DH name so if you want to hyphenate it it should be ok. Her birth certificate will still stay the same but on the medicare card you can add the hyphenated name. I did this with my DD when I married. When they go to school and you are filling in the paperwork they ask for the birth cert but also ask what the child would prefer to be called. So the school will abide by what you write down.

The adoption process should be ruled out anyway because you have to relinquish your right as well and there is no guarantee that they will grant it back. I ruled that one out straight away lol.

Good luck with what you decide.