Yep, I am part of that club, too...
My MIL said, "If that's what you want to do with your life," when we told her we were marrying. She said, "Well, if that's what you WANT to do," when we told her we were having Max.
I recently went on vacation with her, Mr. Tippiechick, Max, Mr.'s nieces, and Mr.'s grandmother. I did not want her getting her claws into him or Max for a whole week. The whole time she made me feel like the worst mother EVER. She did things I don't want to even talk about...
I actually ended the vacation by calling her and her mother huge bitches. My husband saw for the first time in four years what I had been going through. He FINALLY saw his mom and grandmom for what they are and saw what they had been doing behind his back. He hasn't spoken to them since.
It's been wonderful
You have to figure out if there's hope for your guy. If he sees the things she's doing will he put a stop to it or will he try to not rock the boat? You have to decide what you are going to do if he doesn't want to cut the cord.