Jumping in from another DDC...we are in the same situation (2 moms, I'm carrying), so I understand her wanting to give something all her own to the baby. Our babies will have my partner's last name, and she named 2 of the 3. I had a girl name I have loved for years, and we used that, but she chose the rest. However, I had veto power over first names. She chose 2 middle names that are family names for her family...I like one and dislike the other, but it was important to her.
Hopefully you can talk about it, and compromise on using it as a middle name, or a veto clause. Good luck!