o how fun, thankfully, i'm a young stepmom with older step daughter's (14, 13 and 24-i'm 27) i stepped in the picture when my 2 younger step daughter's were 10 and 11??, well, at 12 and 13 my older step daughter, rebelled BIG TIME, throwing her homework in her locker telling mom she had none, calling her sister EVERYWHERE a beeach yelling at mom, tried that with my husband and i....VERY angry, we know why but it's personal, she remained that way for an entire school year. mom held her back, and what her dad and i did was COMPLETE iscolation. when we had them she had to go straight to her room which had nothing but her bed, she refused to bring her school books and home work out, so i went online at work and printed my own homework on her level, she tried to tell me she hadn't gone over that in class (which was all the time-i knew better, she just wanted out of it), i showed her (being better at math in my family) and still made her do it, her break from the bed room was chores inside when family was outside, and outside when family was inside, only after my husband told me what he wanted her doing i made sure it was followed through with, because she wanted the attention from her dad NOT me, so eventually he went in and talked to her, he told her that as long as she keeps it up, she will not see him but for dinner on saturday nights and at church.
well, she's now a straight A student, brings her books out when she has a c so she can bring her grades up, asks for help and well, and told us many times, that she ABSOLUTELY hated not being a part of the family for movie/play time or even doing chores in the back yard with me or her dad while her sister swam, etc. eventually because she threw a fit one day i broke down and told her, if she still was having problems, she needs to step up and talk to someone about it, or shut up and do right...well, i guess not feeling sorry for her anymore (at least dad and i) worked because she don't look for that kind of attention any more
sorry so long...moral of the story, find out what she's angry about, dont' feel sorry for her if she refuses to talk and start cracking down.
some say i'm MEAN and an evil step mom, but ask my step daughter's and my own daughter, yes they HATE it when i am in dicipline mode most kids i know do because i can get HARD AS HELL to deal with. but do right and we can all play and have fun
update based on your update, i think you're confused that you have no control over school............YES YOU DO! you can still punish her at home for what goes on at school, maybe have the teacher send a daily log of her attitude, and start cracking down e-mail me if you wish for ideas.