I don't see a problem. Are you sure she would even mind? If she told you that she wants to use it for a son of theirs one day, then I could see the problem -- and I would be on here "side." Silly as it may sound, I have to feel for a couple who want to call their child after one of them, only to have it used by so close a relative as a sibling. Absent that specific scenario, I wouldn't worry about it.