Okay, this is totally like a situation I had... with one of my sisters.
My sister, is JUST like yours.
ALL my life... she was just a bully, manipulative, difficult, picked on me, NOTHING was ever enough or good enough... and NO ONE COULD EVER PLEASE HER and she just liked to control everyone.
She even told off a school Principal once... because she thought she was right and he was wrong. This was in High School.
Anyway, no, it was no one else's fault. My sister is just a problem and a bully and manipulative and a master at emotional blackmail.
Once I got married, she did that to my Husband too... then when I had kids she did that to them and tried to control my kids and Husband. It was BIG problems. So... I told her off. I cut her off. I told her I will NOT put up with it anymore, I told her she needs a Shrink, that I am NOT HER DOORMAT anymore... and I am TIRED OF BEING THE 'NICE' SISTER... .and it will be over. Period. I told her I will NOT put up with her bullying my Husband and creating marital problems for me.... she actually tried to break us up.. and would bad mouth me to anyone who'd listen, including my parents and my now deceased Dad who was severly sick at the time.
BIG DRAMA all the time, with her.
So I cut her off.
With people like this, being 'polite' does not work. They don't understand that. They are just Bulls.
I stopped interacting with her, stopped going to any functions where she was there, and told my family, I will not engage anymore.
that was then.
NOW... she has 'changed.' She is now a 'normal' human being... she even got Therapy for herself, and I don't know, but I think she has medication. I think, she just had mental problems.
So, now we all get along.
BUT.... I do not, and will not, "trust" her completely... because... I know how she can be and how manipulative she can be. So... that is the caveat.
You have to be smart.
Some people use other's as their emotional "dumpster."
You have to decide, if you want to be a dumpster for someone else... or not.
AND how it not only impacts YOU... but YOUR ENTIRE FAMILY/HUSBAND/ AND CHILDREN.
I told my Husband/kids... that I am protecting them... that Aunty is not well and has problems... she can't be nice.
All the best,
Susan