I'm going to tell my mother that her extension of an invitation to a friend of a distant family member for our wedding was inappropriate
Do you have a limited amount of guests?
Yes, and she just invited someone I never met
Best wishes on your upcoming wedding! Your mom shouldn't have invited someone to your wedding without talking to you about it first. Let her know how you feel about the invitation she made.
She's going to say that I'm controlling and don't appreciate her gesture.
You can't uninvite that person now but you should tell your mom how inappropriate it was. It doesn't matter how she will react to it but you should honestly convey your feelings.