hi BigWideWorld,
It sounds like your mom has crossed a few boundaries with you and other relatives (your aunt and brother).
Yes I've had to sever a tie for my own good. I went almost 7 years NC. It has been almost 7 since I resumed contact, but I would do it again in a second, and my BPD'd mom knows it.
She rarely pushes me, and since I'm ultra sensitive to the abuse, if I even get a whiff of it I'm OK blocking her emails and/or texts. Do I tell her this? No, that would be giving her way too much power. I just block and unblock as I feel necessary.
I've come a long way from the enmeshment of my youth. I do have 5 siblings, so if my mom can't get a reaction out of me, she has other people to torment.
The trick is to not trigger her feelings of abandonment. I am really careful to just give her enough, so she doesn't freak out.

b