I can't stand my son's playmate's mom!?

I have a friend who I used to be very close with. She has a 5 yr old and my son is 4 so the boys would play together whenever we hung out. She, however is single and very promiscuous and makes bad choices most of the time. I love having her boy over to play with my son, but she always wants to include herself and frankly no one can stand her! I don't know how to invite her son to play but not her!