I agree with the others that have posted. A name is something that is a gift from a birth parent and often the only thing a child in an adoptive situation actually owns. Perhaps the child is even named for somebody in her biological family, even if she no longer has a biological family. A child of that age shouldn't make decisons of that scale anyway because they may regret it when they are older. MY suggestion would to keep the name she knows, and as a gift to her from her new mother (you), offer her the opportunity to change it later if SHE brings it up or if she is uncomfortable with it or dislikes it. Your MiL could use a pet name for her new grandaughter if she dislikes it so, and that name could be something that they could share together.