My 11 year old sister is going 'scene'?

she'll eventually see that if she continues with this attitude, she'll never get anywhere and then she will grow out of it. in the mean time, try to influence her with other things that she used to like, take her shopping to some of the stores she used to dress from, play a lot of music that she used to listen to before this phase, stuff like that, and be sure to treat her the same.