It is so hard! My DD is only 10, but she has these issues. Never is anything her fault, always blaming others, and she can be so demanding, and upset, when there are consequences, or things don't go her way.

My only advice is to stick with it. Don't get overly emotional yourself. Say it like it is, what a consequence is (though I wouldn't go so harsh on consequences, but do what you say you will), and how you expect her to act. And then stay calm.

I was reminded of some of this just yesterday. DD had a make-up gymnastics class, that I thought was only an hour. When I went to pick her up, she came out to tell me it was 2, but she had a drum lesson in 45 minutes. I told her I would come back to get her, but she would need to leave 20 minutes early. When I did get her, she was furious, crying in the car, saying she didn't care about drums, only gymnastics, she didn't care about the money for the lesson, she wasn't going, etc. I stayed calm, drove her to the lesson and gave her her clothes to change in the car. She was so mad. I thought it might be her last drum lesson because she can be so hard headed. But I stuck to my guns, said I was sorry it worked out this way, but she had to go the lesson, that I would go in and tell the teacher she'd just be a few minutes late. She told me not to, that she wanted me to stay in the car with her. She very slowly started to get dressed. She was 5, 6, 7, minutes late. But I just sat there, breathing and trying to stay calm. I knew yelling at her was just going to make her more mad. When I did say something she said she was wiping her tears away so no one would see them. Then she stormed out of the car and told me not to come with her. Yet when I picked her up 20 minutes later, it was like picking up a different child. And she even apologized for how she had acted, which shocked me. I was amazed at how she bounced back, something she didn't used to do. Or maybe I didn't give her the chance because her tantrums were nasty and I gave in. But she does bounce back, and we have to trust that they can handle being told what is right, and how they need to behave. Even if their first reaction is scary and angry!

I think what I'm trying to say is, just because they get angry and want their way, we can't give in. Ultimately they will appreciate that someday. But we also shouldn't make a big deal about things that are rational! This is how I expect to be talked to, or there will be consequences. And then walk away. Letting her vent and yell and get into it with you helps her case, not yours!

That said, taking away a practice that affects others, and that makes her happy, imho, isn't the right consequence. It's not fair to the others. And doesn't help your case either, in terms of respecting the commitments she has made. But that's just my take.