And also warn the people at the hospital, because if you don't tell them to keep her out, and she tries to come in, they are going to come ask you while you are in labor and that pretty much will guarantee a scene. Just tell her up front and stop worrying about hurting her feelings. She probably didn't have her mother in the room when she had you, she will get over feeling left out.
Tell her that you would really like for you and your husband to have that experience and bond together as husband and wife and soon after baby is born she is welcomed in
I would sit her down before hand and nicley tell her that this is very important to you and your his dan that you are the only people in the room! It is an exspeareance meant for the parents just gently tell her