I feel for you. My husband has that kind of relationship with his mother. We're speaking again and working on repairing the relationship, but for a while, it was best for us to cut off contact. We just couldn't deal with the manipulation and nastiness. We needed the time away from her. It really helped. Now we can approach the relationship with new patience and understanding and a better ability to distance ourselves from her emotionally while still keeping in contact. You might need some time, too.

Don't feel guilty about wanting some emotional distance. You shouldn't have to put up with someone who makes you feel that way just because they're related. But with time, you might find a way to repair it so that you're happier and more able to be in control of that relationship.

I'm not sure anyone can speak to the specific circumstance that is pushing you in this case. It sounds more like there's a build-up of her comments and behaviors through the years that is driving the wedge between you. Take some time if you need it. Tell her you need some personal space and time for reflection. Be prepared for her to try to burst her way back in, though. She might use that to make more drama. You have to be firm in protecting your personal distance once you set that goal. Don't let cards, letters, phone calls, emails sway you. Simply tell her you're taking some personal time before getting back to her, and then don't respond to her again until you're truly ready. Best wishes with healing and finding some peace.