I’m very sorry to hear of the long, difficult struggles with your mom. But I would honor your instinct on this. You have known since you were a little girl that you mother can’t provide the love that you would’ve liked, and is not likely to get much better in the near future. She doesn’t seem to be seeking treatment and you have become the lightning rod for her discontent.
Your instincts about not wanting to have contact is actually very healthy because you realize that in spite of your help she hasn’t been able to have a relationship with you. The difficulty here is the anger. When we use anger to push ourselves away from other people it creates a turmoil inside of us that causes distress and discomfort with our decision.
This is the time for compassion. Your mom sounds like she has a condition and suffers from much emotional difficulty. The sad part is you may not be able to help very much, and what you need to do is to detach from her with compassion. Compassion is the most important thing. If you do it angrily it’ll make you feel guilty, frustrated, and upset and ultimately pulled back into the situation. Detach with compassion and do what you can do to help, but go live your life. You may also want to try doing loving-kindness meditation. Here’s a link to a sample. It has been shown by research to help with our emotional regulation and well-being.
I’m not suggesting that any of this is easy, but I do believe it is the right path to cultivate.