I am stepmom of an 11 yr girl and I have similar issues too. She doesnt get to go or do what she wants unless her chores are done, homework done, and she hasnt given me any attitude. The rules are the same for all 5 kids so she is not being picked on. Missing tv, phone, sleepovers, and playtime with her friends has made a difference. I have had a few heart to hearts with her as well and try to show how I feel too and how unfair she is being not only me and her father but to her siblings as well. You have to remember, 12 yrs old, she is stepping up to a teenager soon and she sees attitude at school from the other girls too. I found that some of my stepdaughter's friends were saying things about me and how I make her do her homework and chores first and one of them told her to tell me to F**k off! I lost it and I spoke the other mother and they no long hang out. I wish the best!