Hi angel, I'm sure you're not doing anything wrong. I had no end of trouble with my eldest dd (aged 15) over the last 18 months. You will find it all opn the teenagers threads. She went right off the rails and let her school work slide, she didn't care about anything, refused all support and help from us including allowance, lifts, even stopped coming downstairs for meals.
I was in despair particularly over the way she spoke to us - nothing we ever said was right and she was so rude and hurtful. There were many times I thought the situation was hopeless and that I had tried everything. But I knew I couldn't give up because I think she was testing us to see if we would love her no matter what. If we had given up she would have never got over it. It was really tough, but I had some fabulous support from mumsnetters. We found some ways of giving her more adult freedoms and she gradually changed. As if she had left the human race for a while and then slowly found her way back.
It must be terribly confusing trying to find one's own identity in the world, especially for children like my daughter who unfortunately had had a very high number of bereavements and sadnesses in her life. Her own father treated her appallingly and part of it was the backlash from that. She has had a stable home with myself and her stepfather for seven years now, but so much damage as a little child had to show itself sometime.
She is now still moody and rude sometimes, but not on the same scale as it was. We often have fun together and do things together now, and she is more willing to join in with family activities again. She had to work very hard to catch up with her school work and I think it has taught her a lesson about long-term planning.
I found the school very helpful with this - they wouldn't let her get away with not completing coursework on time and she had countless detentions for catching up. She soon got tired of that.
They do put a lot of pressure on them with the GCSEs looming and perhaps your dd is buckling under it. If she feels the situation is hopeless she might well feel like giving up. They have so much to do nowadays.
Perhaps you can liaise with her head of year. I found my daughter's school staff very helpful and they were glad to be approached to discuss the best way of encouraging her.
I well remember how for months I couldn't talk to her because she would turn everything into an argument. She also used to treat her younger sister horribly. I think she is now realising how nasty she sounded and trying very hard to get out of the habit. I actually find I like her again .
I hope you can find a way of giving her the support I know you want to. It's so hard when they won't let you, isn't it? I found a good way to breach my dd's armour was to find something she really liked doing and do it with her (going out for dinner, for example) and make sure I didn't talk about any problems we were having while we were doing it.
Good luck!