When kids act out, and most of them will....there is usually a REASON. There is a reason for every human behavior. Whether it's open defiance, opposition, passive-aggressiveness. Maybe she is not getting all her needs met, but doesn't know how to go about asking for that. I think most kids [deep down] have a desire for their parents to be together, not apart and not with someone else. "I wish my mom and dad were back together and we could be a happy, normal family". Going between two households is hard too. She's got three parents here: You, her dad, her mom.
It's okay for her to protest, it's okay for her to verbalize, to question. It's not okay for her to kick anyone, though. I wouldn't get into any power struggles about clothes unless she wants to dress in a highly inappropriate way. But, at this age she is going start having certain taste for what she likes in clothes. I remember when my daughter started to get VERY PICKY about what she would wear. My mother didn't really tell me what to wear by the time I 8 years old.
She is an individual and is emerging with likes, dislikes, troubled feelings...maybe she is really hurting inside and doesn't know how to express it. If you stop and think about, her situation sort of stinks at times. She's goes between two households, two parents, each different. You know what it's like to juggle a few things at once as an adult. Kids haven't developed that maturity yet. They're kids. When life upsets them they tend to act out.
I am all for counseling.
In the meantime....you as dad's live-in girlfriend/stepmom need to try and not take what she does personal. She is 'acting out' and kids do that a lot.