I agree with you totally that it is your daughter and future sil 's wedding. But Mary Margaret I think you are wrong when you say you will not have a relationship with her. What about when your daughter and sil have children? Are you not going to be apart of your grandchildren's lives? She will be their grandmother also and probably be apart of their lives. Thus you will have a relationship with her for the rest of your life unless you do not plan on attending christenings, birthday parties, ball games and etc. Remember she is your sil 's mother and that will never change. Hopefully this is just due to the stress of a wedding and she will calm down or I pitty your daughter.