My mother is also insane - she has borderline personality disorder and is bipolar. A fun combination that made for a chaotic childhood.
Did you watch the new "Maron" episode on IFC? If not, it was pretty good - it was all about his crazy dad and unstable childhood. Really hit home for me, especially when he said that there comes a time when we must give up on the fact that our parents are going to be who we want them to be - when they fail, we must parent ourselves. Sad, but it was true for me.
Honestly, and I am not advocating this, what helped me most of all was not talking to my Mom for a year. She had an episode during a holiday that resulted in my (now) ex throwing her out, and rightfully so - she was completely out of control. But it helped me step back and see that I had very weak boundaries when it came to her. While I wish the event hadn't happened, it really helped me step back and re-evaluate my relationships and boundaries, and that has helped me a lot.
I guess my point is to take a step back when you feel overwhelmed. I am not saying do not talk to her for a year, but maybe don't answer the phone or see her for a day or a week if it is just too much. You need to take care of you, first and foremost.