The YOT/EP development sounds positive, Couthy. :) The rest of it sounds less good - not bad, but a bit "same pls, same old; here we go again". I'll keep my fingers crossed for you tomorrow.
I'm wondering... You are, clearly, an extremely strong woman. (So am I). You also clearly have an intense relationship with your first-born. (So do I). The teenage years are all about separating emotionally from parents and becoming independent, and it has occurred to me before that children who have strong relationships with strong mothers may have 'further to go' to grow up, and may feel (unconsciously) they need to fight to break free. When my DS1 was your daughter's age, I certainly felt like he rejected everything I had to offer him or found it wanting, and that he rebelled about everything I thought was important, fought against all my expectations of him, and rejected all my personal values. It is hard for parents (and perhaps especially hard for single parents) not to have in their heads some notion of "a child of mine will be like this and do these sorts of things" - and a child who feels they need to fight for their independence has a pretty good template of how not to be, IYSWIM.
And it's hardest at 15-17 IMO, because you are still responsible for them, and can see they're still so young, and all the things you can possibly try to 'control' their behaviour give them the impression you are trying to hold them back and stop them growing up...
I think this is partly why Maryz's advice to 'detach' works well - because if you can manage it, you create a bit of emotional distance, and the child who previously felt s/he had to fight tooth and nail to break free now feels you may not fight tooth and nail to hang on to them.
My son was almost 17 when I had him arrested for assault and criminal damage, and refused to have him back (tho like you I let him home just before his birthday). I wonder whether it would be worth you trying some of the things I tried, which seemed to help us...?
Firstly, just the fact that we'd had a break from each other meant that we both began to imagine life living apart. I think this meant we both felt less panicky about the idea that we were condemned to live together for all eternity .
I re-negotiated some symbolic freedoms, using the birthday to do it. E.g. "Now you're 17, you can come home whatever time you like at weekends, so long as you let me know..." and "Now you're 17, I I know the extra year is significant and you'll need to find your own appropriate 'freedoms', but generally, I took my clues from him - i.e. I relaxed the rules where he had been fighting me most.
After he'd felt the benefit of these freedoms, I announced some up-coming responsibilities, e.g. "When you're 18, I won't give you pocket-money" and "This summer, since you're 17, I expect you to get a holiday job if you want more than £5/week"...
I talked often about "When you leave home..." and "When you have your own place...". This was sometimes part of a nag - e.g. "When you leave home you can make as much mess as you like, but meanwhile..."! - but I also tried to use it positively - e.g. "When you leave home, where do you think you'd like to live?" I honestly think that, deep-down, my son thought I was never going to let him grow up, so imagining an independent future helped a lot to make him feel he didn't have to fight me so hard.
I reckon some/all of this might be worth trying with your DD, Couthy...? :)