It's possible that removing her from the social scene she feels so comfortable with would do more harm than good with regard to her studies. While I understand your concern about her apparent loss of the thrill of learning; I wonder if she isn't simply focusing on a less academic, but equally important area of study...her social life. If so, it doesn't mean that she won't find her way back to enjoying her classes. It may just be one of those things kids need to do as they learn to flex their independence.
I'm not trying to discourage you from homeschooling; but at her age she definitely needs to take charge of her educational future; and that includes having a say in where she attends school.
One online program you might want to check out is Keystone High School
http://www.keystonehighschool.com/They offer single courses, a general diploma, and a college prep program. They also have summer school courses, so you could give a class a try before making a decision to enroll full time.
Best of luck!