K.T.
Is this a sudden behavior? If so, she may be picking up some anxieties about moving to another state, leaving friends and family behind, issues in school, etc.
If it's just a natural progression of behavioral issues (since you used the word "stubborn", I'm making an assumption that things have just reached a boiling point), I would recommend "Setting Limits with Your Strong-Willed Child : Eliminating Conflict by Establishing Clear, Firm, and Respectful Boundaries" by Robert J. MacKenzie.
I have a STRONG WILLED (yes, I meant to capitalize that) darling only son, who used to think it's his way or else - he has actually told me "You're not the boss of me". After reading this book, I found ways to teach him that I am his his guidance counseler, his loving parent and sometimes his boss all in one. He has learned that yelling at me to do something is a surefire way of getting me to *not* do it, so he quickly apologizes and asks in a nice tone.
It's a long learning process on both ends not to engage in a dance of wills. Both sides need to change their actions for it to work.