Friend-relationships and when friends won't let a truly toxic person go

Basically, there's this girl I was formerly friends with who turned out to be, hands down, the worst person I have ever met. She honestly displayed disturbingly sociopathic tendencies, as exaggerated as that may sound. She's selfish, cruel, completely lacking any empathy, narcissistic and secretly violent. When I first became friends with her a few years ago, she quickly established a power hierarchy. She essentially made it clear that she was the frontrunner and that I was a "sidekick", and that I would be nothing without her. She would constantly make underhanded remarks that were basically used to remind me that I'm "inferior". It would be little things to undermine my confidence, like boasting about how attractive she thinks she is, then adding that I'm okay looking but less attractive: "I'm definitely a 10. Oh and you're not bad. You're kind of, like, a 7.5". She would also do things like sneak into other people's dorm rooms and steal money from their dressers or poke holes in their condoms, or steal money from charity donation boxes. I always witnessed her blatantly lying to other people about jobs or grades or money, but I guess never really imagined she would lie to me about anything. I know it's stupid in hindsight. I sat by while she did a lot of really messed up things that she played off as "just a joke". I was a freshman in college and brand new, and she was always bragging about how she was "popular" in high school. I think I was caught up in the novelty of finally making friends and connections. Some time later, her behavior towards me escalated. When I lived with her, she started stealing money and other valuables from my room (even though unfortunately I couldn't prove it). She stopped paying rent and guilted me into paying her portion of it. She started spreading rumors about me to our mutual friends and to other people, a lot of ridiculous lies. I think at this point, I didn't stand up to her because I was afraid of what she would do. In the past, I had seen her purposely crash into other people's cars if they took parking spots she wanted, so I didn't want to imagine what she would do to me. She also started having violent outbursts towards our mutual friends. She would scratch or hit or throw heavy objects at them if they said something she didn't like. She started becoming possessive and manipulative of her boyfriend. For example, when he was searching for an apartment, she actually called up the landlord behind his back and convinced him not to rent it to her boyfriend because she didn't want him living so far away from her. Our circle of friends just overlooked all of this as her acting out again. I'm not sure how we ever justified her behavior. Maybe we were secretly a little intimidated. A little over a year ago, I finally cut her out of my life for good when I found out she was having a fling with my boyfriend at the time. Funny enough, when I confronted her about it, she tried to guilt me by saying "it's none of your business what we do. Now you're telling everyone and making me look like some kind of horrible person." The conversation ended with me actually apologizing, but I never spoke to her again after that day. Maybe two months after this, one of our mutual friends informed her boyfriend that she had been cheating on him with multiple people, and she essentially lost it. She physically assaulted this mutual friend and his roommates. She ended up getting arrested and charged for assault. Her boyfriend chose to stay with her, but she ended up being arrested maybe 4 or 5 times after this for physically assaulting him when he would try to break up with her. At one point she pulled a knife on him, after which he got a restraining order against her. Of course, that didn't stop her from smashing his bedroom window with a rock or breaking into his apartment and waiting there for him to come home. After she decided to stop essentially stalking her ex and came to terms with the fact that she no longer had a place to live, she started cozying with what used to be our mutual friend group. The problem is, I've cut her out of my life completely, but some of my friends refuse to do the same. They know the foul things she's done to me and others, and yet they still insist on letting her back into our lives. It sounds petty, but I'm a little offended by this. It feels as if they don't have my back. I never ask people to pick sides when it comes to personal conflict, but this is different. They fully know the horrible things she's done, but they are still so willing to overlook it. This makes me feel like they don't support me or have my back. It sounds even pettier, but part of me is also upset that she thinks she's somehow "won". In her mind, she believes she's done nothing wrong and came out on top with all of these friends. She has not even acknowledged the things she's done and still tells people I'm the "crazy" one who should be avoided. It's actually unfathomable how delusional she is, and I wanted this negative energy gone from my life forever. Apparently, that might not be possible if this handful of my friends keep inviting her back into our lives.

Oh please keep away...