Yes, mother. CPS nearly pulled me out of the house while I was in kindergarten and if her side of the family had been a little lower on the socioeconomic scale I probably would have gone into the foster system; they knew exactly which hoops to jump through. When the parents divorced I insisted on living with Dad. Tried to maintain a relationship with her out of respect for other relatives who didn't realize exactly how bad she was. Yes there was a final straw, but in retrospect I would have cut off contact with her sooner if there hadn't been huge amounts of pressure to keep trying.
The last time I visited her was twenty years ago. The last time we spoke was fourteen years back. Polite distance didn't work.
Haven't regretted it for an instant.
A thread like this is sort of a message in a bottle to younger people in similar situations. So a few thoughts in a more general sense.
It's natural to want a good family relationship. But if they make out like you have to be flawless before they'll do the rudiments on their end, it won't work.
Do you like the sides of yourself this person brings out?
People who are difficult under the best of times tend to get worse under stress.
Is this a person you would avoid if you weren't related?
When people tell you you'll understand when you're older have they made an effort to hear you out first? Or is that ageism you're hearing? Listen critically: for example if you've accomplished something at great personal effort in spite of the difficult relative, and they try to credit the relative for your success.
Do you feel a moral obligation to shield any children you have (or any aging or disabled relatives in your care) from this person?
It was the last of these that really did it for me. I tried to reconcile when Dad got terminal cancer and she exploited the lines of communication to torment him. Had to cut that off fast. Had gotten inured to bad treatment for myself, but there's a protective side of me that just won't tolerate seeing a helpless person suffer needlessly.
She's got the money to pay for professional care in her old age. And to be frank, even if I were willing she wouldn't accept help from me. Too much of her ego is invested in being contrary.