Onlyme - I have a daughter of 11 and she is the same - I think this is normal for girls of around this age - stroppy, argumentative for no reason, giving lots of "evils" (a la Vicky Pollard), lots of door-slamming, tuts, muttering, being unreasonable and generally a pain in the arts. But then, an hour later, my bestest friend.
I think they have a lot of hormones going round and feel a lot of pressure from school, peers, older kids. Think there's also a lot of frustration as well - they're too old to act cute and naughty, but too young to have much independence.
I try to treat her like a young person, not a little girl - I talk to her as I would anyone else, explain how her actions make me and others feel, how we like to be treated as we treat others, the usual stuff I spose. She's still a little witch when she wants to be!
It's something I think most mums (and dads) have to put up with, we just have to try to step back, take deep breaths and the odd glass of wine!
I sympathise with you and, if you do find out the way to sort it out, please let me know! x