Payback is a bitch and so are you

May be, it was just my thinking.

A little back story: My dad remarried when I was about eight years old, to a psychotic woman, and out of that, my brother and I ended up with four almost equally psychotic step-siblings.
I've realized now that it was mainly just my step-mom's doing. She was a pretty bad alcoholic for a time, was horribly jealous of my dad spending any time with me (I was 7), refused to include mainly me in any family activities/trips/pictures, had my little brother and I sleeping in a bunk bed, in a laundry room with no cooling whatsoever during the weeks that we'd spend at their house during the summer. I live in Tucson, AZ. Coupled with the dryer running most of the time, it was horrible.
Anywho, one of my step-sisters got into being a huge meth addict around the age of 14. She was the worst.
Ridiculed my brother and I, sexually abused us on more than one occasion, constantly made fun of pretty much everything about me...

One day, I got sick of her shit and called her a bitch. Apparently, it was bad timing.
I had no idea that she was tweaked out of her mind when I said it.
She launched herself with meth-like reflexes across the living room at me, arms outstretched, and her hands clamped tight around my throat. Next thing I know, my step brother had thrown himself into her and it surprised her enough to release her tweaker superhero strength from my esophagus.

She's since cleaned up but she's still a crazed nut job who does anything she can to play the victim in any given situation and bullies people until they give her what she wants. Three kids have made her only slightly less selfish.
Anyway, tonight she posted on Facebook that some dude gave her a hard time about not being able to put store credit on a gift card, and after her final "no", he jumped over her register and grabbed her by the throat.
I know she's slightly better than she used to be and she was just doing her job. No one deserves to feel unsafe at work... But after everything, I felt a weird sense of satisfaction that she was getting to understand the terrified, helpless feeling that I'd felt.

Tl;dr: Stepsister was a crazed meth head, OP got sick of her shit when she was little, called her a bitch and stepsister choked her. Tonight, sister was working, angry customer tried to strangle her and OP was oddly okay with it.