First, by telling auntie and the others "Don't tell mom", *you* are putting them in the middle of your stuff. Sorry.
I am right where you are. My mother has undiagnosed mental illness, refuses to get help, and I've had to make very hard and painful boundaries with her. I've also had to deal with discovering that my step-mom sent birth announcements and information to my maternal grandmother, who has nothing kind to say about me. (She and mom are enmeshed.) I felt a bit helpless, but realize that there's nothing mom can do that unless I let her. I own my life now.
It really helped me to have a counselor to talk to about all this. She offered support, perspective, and also insight into the traits of those who suffer from the same mental illnesses my mother's behavior suggests she suffers from.
For what it's worth, you have to come to a place of peace in your own soul, and this is ALL you can do. Let your actions with family members counter any lies mom is spreading. The lying is really about her: her anger, her helplessness. My mother still claims that I'm a petty little person who isn't speaking to *because she didn't give me Grandma's Christmas present*. For over ten years now? right....
I really feel for you. It does get better, though. If you don't have someone to support you, find a good counselor or a wise friend who can advise. I truly love and miss my mother. I'm very sad for her that she's so stuck, she's ruined her own life. But I won't let her ruin mine, nor my son's.