Good Morning! This sounds like an extremely complicated situation with quite a history attached, and I can imagine how painful it is for you to manage. The basic message I get from reading is that your daughter is rebelling in a powerful way, and is very fearful of being controlled (however, inside, I am guessing that she is hoping for someone to be strong enough to be able to contain her ever-growing rebellion) . She has somehow learned that there are no boundaries for her behavior and although she acts as if she is hardened and cold, she is self-protecting and covering up a multitude of personal vulnerabilities. My favorite stand-by phrase is that 'we teach people how to treat us"... and if you have tolerated her behavior in an effort to keep her in your life, as if she sets the terms on how you will relate to one another, this must now stop.
Tough love isn't easy to do; yet, to simply tell her that you have reached your limit and that once she is ready to have a mature conversation about what she wishes to be different, and what she is looking for help with, you will then... and only then, be able to help her. Otherwise, you can no longer tolerate the abuse. It will feel like you are abandoning the relationship for a bit, but this isn't permanent. It is called putting down a boundary and following through on holding it firmly.
She needs firm leadership with an understanding and caring, yet firm approach, with a focus on setting goals for what she wants her future to look like.
Yet, sadly, the most important answer here is that as much as you want her to change and have continued trying to help her, the truth is as you stated; you can really only control yourself. All you can do now is to keep the hope alive that there will be someone who can reach her soon, or a circumstance that will occur to teach her the next lesson. For now, keep supporting the school's efforts to reach her, and don't give up on her, but set some boundaries for how she will treat you, personally. It will take time and strength, but all things change with time. If she can consistently see you as a source of love and support, yet knows she cannot abuse the relationship, this may be one of the things that begins to change and repair her relationship with you.... as well as with herself. My very best wishes to you on your continued hard work ahead!