Actually you've given very little information here, and some massive drip feeds that mean people are, understandably, changing their minds!
My feeling is this:
In a marriage, both parents have equal say and power of veto on the names of children. In this case, the fact that you decided at 11 that you would name any future daughter you had after your mother, with no discussion, would carry no weight with me, I'm afraid. I don't agree with naming children after other people. They are individuals in their own right and deserve to have their own name.
In your situation, however, I would say it's the opposite. I would chose the name, and I would give my surname. Both of my children were born when I was unmarried and they both had my surname. It wasn't even up for discussion. Future MIL had something to say about it but I said that was my decision and it wasn't up for discussion.
The baby wasn't planned, you hadn't discussed names, you don't live together, your finances are separate, you won't be getting married... how long have you been together, exactly..?