Getting ready with bride.

My sons fiance has asked if I would like to get ready with the wedding party. I said yes!!! But I now realize that my sons ex- stepmom, who he is close with, is also going to be getting ready with them and she hates me. She insist that she is his mother and that I do not exist. What do I do? I do not want to hurt anyone's feelings but I also don't want to put myself in a position where I will be hurt.