I'm not saying she's not capable of living a normal life. I think she is, but she sounds like she's got more than just OCD going on. (She's showing some classic borderline personality traits for instance, not to internet diagnose her though.)

Your childhood, and your parents sound absolutely awful.

I'm in the UK so the system is different here. I think what you first need to do is to find out what sort of support systems can be put in place. In the UK the process is speak to your GP and they will refer you to other resources. My GP was the one who got me a social worker, and a psychiatrist referral. My social worker was the one who was able to help with my housing situation when I got kicked out as a teen, first finding me temporary accommodation and then somewhere more long term. I have absolutely no idea how to go about this in the USA.

Hopefully there is a way you can find out? Does domestic violence have to be a partner? Because the situation with your parents sounds violent, if not physically then mentally so. If nothing else those resources might be able to point you in the right direction. Or are there homeless resources? Or something mental health related? Actually does your city have a subreddit? Could you ask there?

You're trying your best I know. I don't think the situation is going to get any better with her staying with you. And it seems like it'll drag you down with it. You survived getting kicked out, right? She likely will too. It can be so terrifying to see someone you love self destruct in that sort of way but if you've done all you can to help and it's not working out you have to put yourself first. Which I know is so hard if you've grown up in an abusive situation as you have, and you have all the traumas related to that.