Maybe next time she suggests a name and focus on it. Say, so you really think that "Mavis" is a really nice name, OK we will consider it, but aren't making any guarantees. That way at least she thinks that she is being consulted. And she will be focussing on that name rather than any other suggestions that she made.
That could work I'd try it depending on if you think she'll remember the Isabella thing being her suggestion cos personally I couldn't stand hearing how "it was my idea" it would drive me nuts!!

Good luck!