T.,
Twelve is a hard age. I had a very functional, normal American, Christian home - and I haven't forgotten Twelve. The hormones must play havoc at this time because a twelve year old girl's reasoning goes haywire. You cannot reason with them...you can talk intil you are blue in the face and they will shift blame and come up with a "But..." every time. I did it...my daughter did it (my sons, didn't - hummmm) and now I see my best friend's daughter doing it at that age. She is a really, really good girl...but she gives her mom STRESS!!!
Maybe focusing on this, responding to her warmly as you are able and continue doing what you know is right will help you emotionally wade through this time.
Warm, loving responses are the key to YOUR emotional stability (it makes you feel more confident) and it will help you wade through this - possibly putting a lot less strain on your relationship with her.
I promise you - twelve years old (and younger and older) are begging for you to control them for they are not mature enough to control themselves. They buck the boundaries...but they are screaming inside for you to set them.
I would often say to my daughter (it only works if you say it firmly and calmly)..."we'll continute this discussion when you are in a better mindset"...OR..."That's enough. End of conversation."
If it is not about the little ones - at twelve...she will find something else. It's just life for a twelve year old.
J.