Welcome to the wonderful world of hormones, puberty, and middle school girls. We have a 12 year old Princess Sassy Pants too. Mine has ODD, ADHD, and is extremely intelligent. She thinks that she's equal to an adult in her decision making skills and doesn't think childrens rules apply to her. She's felt this way since she was little.
We're also very strict with her, although I think I'm more disciplinarian and lean heavily toward natural consequences. Last night she broke three serious house rules (lying, blaming her sisters for what she did, being severely disrespectful to me, plus one or two less serious house rules). She was rude and disobedient to boot. She was caught red handed in her lie, so I told her that I'd remove the privilege of the school dance this coming Friday, no Trick or Treating, no cell phone, and I'd remove the door off of her bedroom if she didn't come clean.
Not only did she come clean but she copped to two other things she had lied about that I DIDN'T know about but were serious. So I knocked her discipline down to no video games for a month and her bedroom door must remain open at all times unless she's naked for three months. She apologized on her own to me and her sisters. She attempted to make reparations for what she had done as well without my having to ask.
We did some talking, of course, because she's a talker and she responds best to conversation. These things were laid out as options to her with explanations that each disciplinary action was for a separate issue. I gave her some time to cool off before she decided to come clean.
You have to be okay with your daughter saying, "I hate you." You have to think to yourself, "Good, I must be doing something right." We're not our childrens friends, we're their parents for very good reason. They can't parent themselves.
EDIT: I do want to clarify that I come down harsh initially because my eldest daughter likes to bargain. She looks for loopholes in everything. If I "over punish" or "over discipline" then I can allow my daughter to "work me down" to a lesser disciplinary tactic that I would have used in the first place. She's still not happy, but she can live with it.