Mother-in-law Hell

My MIL has always been a pain, but today I feel like I am finally done with her. She’s done things in the past such as bringing up painful/hurtful situations that are better left alone, and seems to enjoy revealing other people’s weaknesses or issues, while ignoring her own. Last night she sat my son down (he’s 18) and said that she’s been lying to him for his entire life to protect him (from what??!!), so it was time to tell him the truth since he’ll be leaving for college soon. I haven’t gotten the details from him yet, but he said it was just a bunch of messed up stuff. I’m sure it had to do with what a horrible mother she thinks I am or whatever problems I’ve had in the past that my son would never remember because he was little. Now that my husband and I have been really happy and have a great life, she seems to want to mess everything up for some reason, instead of just being happy for us. Last Easter she started this crap and tried to bring up a bunch of old issues and ruined the day for all of us. Even my FIL told her to leave well enough alone and asked her why she was trying to dredge stuff up. If I actually told her all the stuff I thought about her or how we all really feel about her, it would blow her away, but I’ve tried to be the mature one, trying so hard not to be like her. She is so lazy and awful to everyone and expects everyone to wait hand and foot on her while she sits there and pontificates about everyone else’s lives. I want to tell her that my daughter can’t stand to go to her house, but we encourage her to to be nice, but I don’t. I don’t want to have anything more to do with her!