How do I deal with a sociopathic sibling? Please help.

Hello!! So sorry, this will be a bit of e vent-like post. I just really need some help.

I've grown up forced to emotionally raise my sociopathic little sister. I was parentified and emotionally neglected very young, and I'm finally at a breaking point.

My little sister is horrible to others. She has bullied me relentlessly growing up, and then called it joking when I was hurt. I've been called too sensitive by her a countless number of times. I kept forgiving her, but now, I really need some help. She's in her early teens now, and no change has been recognized whatsoever.

She has several traits that make it so hard for me to get along with her. Selfishness, laziness, attention-seeking, constant copying of everything she sees and hears from others (up until even her now very very early teens, and my LATE teens), she's highly insecure, extremely opportunistic, even if it means hurting others, she's inconsiderate, dismissive, you name it. And i'm finally going nuts from it.

My entire life, I've blamed myself for the way she is. I thought it was my responsibility to raise her, and I must be doing a bad job ​for the way she is. I really want the best for my little sister and I want her to be happy, but I can't keep raising this child who was never mine to raise. But now.. I've realized she is never going to change. I've offered grace and forgiveness a countless number of times. And now I'm realizing I just need to accept this is my little sister. I can't control who she is. That's not in my place. So, I established a boundary, where I would use the Grey Rock method with her until I noticed any signs of change. And so far.. none. See, she mimics change by taking behaviors from others that are rewarded positively, and will only mimic this until she gets what she wants. Then, she just drops it, and goes back to being how she usually is.

And she's just been doing this mimicking thing constantly. I had hope, and I held onto it.. that maybe my sister would see her wrongdoings and change. But the thing is, she doesn't even RECOGNIZE her wrongdoings, because it's just herself. She's constantly gaslighting and manipulating. I just can't take it anymore.

So sorry if this just seems like I'm only trying to badmouth my little sister. I promise that is not my intention at all; she has her handful of good traits, as well, like her high-energy and how playful she is with kids. I just really, really need help. I can't take this anymore. What do I do?