Uninvited Grandma

I am hostessing a baby shower for a friend. I made it just “the girls”. Our groups of friends used to be so close, but recently some of us have moved and we don’t get to see each other nearly as often. Both the mother-to-be and myself thought it would be great for us to have a chance to get together like we used to before she has a newborn on her hands.

The mother-to-be’s mother just invited herself.The mother-to-be and I also think that she may be planning on inviting a few other family members. What is the etiquette for this? It isn’t just that it was meant to be an intimate gathering of girlfriends. (though this does irk me) I also have very limited money and also limited space. My mother knew exactly how many girls I was inviting, and said she would love to let me use her basement for the event.

HELP!