You may be in for a tough year, kansas, but there is hope!
My DS1 was very like this a year or two ago. He under-achieved in his GCSEs even more badly than your DD, and ended up on a level 1 bricklaying course he didn't really want to do, and which bored him after a few weeks. His attendance dropped, he became very disengaged, he hung out only with other disengaged YP, took drugs, got himself arrested a couple of times... His attitude was terrible and his self-esteem was worse... :(
Imo, it is a vicious circle: the less they do, they less they think they can do. They end up losing all their aspirations and believing they can't achieve anything worthwhile, so they might as well not bother at all.
However, if they're bright, and there is some self-respect buried somewhere under all the bravado, then I think for most of them, it's just an age/stage thing.
Three things happened with my DS to break the vicious circle... Firstly, he got really bored. Summer (last year) was truly awful from my point of view - just dossing about, taking drugs and awful attitude - and at first there were plenty of other people around to keep him company. But when the new term approached, the people around him had plans, and that made him think...
Secondly, I reached my limit. I had barely managed to hang on in there for 9 months, and I realised I simply could not stand another year of it. So when he announced he wasn't planning to get a job OR enrol in college last Sept, I gave him an ultimatum, and told him that if he wasn't in a job or on a course - not just talking about it but actually doing it - by X date, I would throw him out. And I meant it.
Thirdly, he just grew up a bit! 
Now, a year on, he is on a course he likes, volunteering too, and talking about university...
It'll happen with your DD too, OP, I am almost certain! At some point in the next year, she'll get bored, or you'll reach your limit, or she'll grow up, or all three... And she'll be back on track. :)
Meanwhile, you need to look after yourself, because it's incredibly stressful dealing with a teen like this, and you need to still be alive, sane and well when she comes out the other side!
Good luck :)