The hard part is over.
I'm matching you with one of our specialists who will be calling you in the next few minutes.
I'm sympathetic to your mother; I really am. I have major depressive disorder myself. I know your mother didn't ask for this disorder, and it is not her fault. But she is responsible for her behavior. She certainly can say "thank you" when appropriate. She can listen when someone else talks.
I wonder if it might help for the two of you to have some family counseling? You need to learn to not let her get you down and she needs to learn that she can control her behavior, even when she can't control how she feels. A trained third party could perhaps help you both.
If she has been behaving this way for 30 years, changing is going to be really hard (unless she really wants to).
What is keeping you from getting away? Sorry for so many questions but it is all relevant.