How to politely ensure an uninvited guest won't go to a baby shower

Hello,

My mother is planning our baby shower and we were going over the guest list.  Unfortunately, my youngest sister came by & put her bf on the invitation list.  My husband, family and friends do not like him & have made it clear he is not welcome in our home. I need to figure out how to tell her, we do not want him at our shower.  There is some very bad blood between all of us but I don't want my sister to take out her anger and frustation on the family, my husband or I.  It may come down to letting her know she doesn't need to come if she refuses to attend without him.  How do I do this?