I was wondering if anyone has any words of wisdom, amazing fool-proof tricks that work or general advice as I've exhausted all avenues and am at breaking point ...
DD will be 8 next week, she has an identical twin sister. For the last 6 months or so her behaviour as gradually deteriorated to what is now unbearable. She is unreasonable, disobedient, stroppy, constantly angry, rude, horrible to her sister and impossible to live with.
Example: Thursday am, I heard them turn their alarm off (they share a room) so went in to say good morning etc. As soon as I enter the room, she starts shouting that she didn't want her sister to call me into their room and would not listen when I told her that I didn't hear anyone call, I just came to say good morning. The next hour was spent with her refusing to get dressed, complaining about everything (too cold, too hot, tights too small, skirt too big etc etc), refusing to eat breakfast, refusing to do anything to the point where I had to shout at her as we would be late for school. This caused her to scream, howl and cry all the way to the school gate when she miraculously got over herself and went smiling into the classroom 
This kind of behaviour goes on every morning, every day after school, every weekend and is ruining all family time. We've tried points/rewards system, she doesn't care. I always give warnings and then follow through with the punishment (DH NEVER follows through) - this usually results in her sobbing and saying 'I'm sorry mummy, I'll stop now' repeatedly after she's lost the privilege.
She is very smart and a model pupil at school. I'm wondering if she's emotionally immature as she can't control her anger at all, and doesn't seem to have the ability to stop herself when given warnings, even though she really doesn't want to lose the treat/privilege etc.
Sorry for going on but I really need help with this, esp with bday and Xmas round the corner