My suggestion (and do take it with a grain of salt since, though I've taken child psychology classes including one that focused on teenagers and I have supervised kids of various age groups, I have no children of my own) is to allow yourself into her world. Learn about whatever subculture she's most interested in. Show interest in what she's interested in. Listen to the music she listens to (and DON'T censor it; that'll just drive an unnecessary wedge between you two), and try to learn about it.
Of course, unless she welcomes you in, don't actively try to join her circle of friends. Keep it between the two of you.
In terms of discipline, NEVER raise your voice, and keep the consequences of what she does logical. Draw a line, and stick to it no matter what priceless treasure she throws across the house. Make sure there's no ambiguity, but pick battles wisely. If she thinks she got away with playing on a computer 'till the wee hours of the morning before class, let her think you don't know, and let her learn on her own what happens when you do that.
Remember that grain of salt.