So my mother had six miscarriages. The baby she lost right before me was a daughter who she and Dad named Old Fashioned Name. I have said for as long as I can remember that I want to use Old Fashioned Name should I never have a daughter.
My cousin is pregnant. Independently from one another, she and her husband both decided they like Old Fashioned Name if they have a girl. Cousin asks my mom how she feels about this (but please don't tell anyone what name we're thinking of). Mom isn't quite sure how she feels about it, but lets Cousin know that she will have to talk to me, too, since I've always said I wanted to use that name. Cousin, evidently, had no idea about that.
I told Mom I was fine with it b/c there is no guarantee I'll ever have any children, much less a daughter, and even if I do, my daughter and Cousin's daughter would be years apart age wise. (I'm actually a little upset, but that has more to do with the idea of never having kids, which is becoming ever more a possibility.) Mom said she was going to have to keep thinking on it b/c while it's kind of flattering, she had also never considered that someone else in the family might use that name and she doesn't know if she can handle hearing Aunt constantly say, "Well, OFN is doing this" or "OFN was so cute the other day, she..." and know that it's not her little girl.
So props to Cousin for thinking about Mom, but I don't know if Cousin considered that Mom might actually have a problem with it.
I think it was sweet of Cousin to check, but at the same time I don't think it would be reasonable of your Mom to say no. I think if it would upset her she should say so, but she should also acknowledge their right to use the name. I think the most she could say would be "To be honest it would take awhile for me to get used to hearing OFN, when I hear OFN I think of my little girl, but it is a beautiful name and I understand if you decide to use it. Thank you for considering my feelings." Because the question is, how would she feel if she tells them no but they decide to use it anyway, seeing nobody owns a name?
I don't think Mom is going to say no, I believe she feels that would be unreasonable and a little silly. I think she'll probably just share her concerns and then tell Cousin to do what she thinks is best. And there's still a 50/50 shot she's having a boy and the whole conversation is moot.
Update: Don't know what answer Mom gave, but Cousin had a boy. His name is Peter, for her husband's deceased father.