This sounds a lot like the things people said about me 8 years ago when I started dressing gradually in all black and "turned into a goth". So although I don't know your friend or you, I'll try to explain it from my point of view when people I'd been friends with for years suddenly wanted nothing to do with me simply because my taste in clothing changed. Just because your friend decided to start dressing differently and listening to different music, etc, doesn't mean that SOMEONE ELSE changed her. Maybe she had an interest in those things before and just never really told anyone about it until someone else (the new girl) with the same look, taste in music, etc came along. Give your friend some credit, I seriously doubt that she changed only because some new person came to school.
Just because you don't necessarily have all of the same interests anymore doesn't mean that's a bad thing. You can still be freinds with people who you seemingly don't have that much in common with. I'm a goth-type who listens to rock music, spends too much time on the computer, hates most sports, and despises pop culture. My best friend thinks everything in the world should be painted hot pink, loves football, thinks pop music is the greatest and is extremely social. Most people would never guess that we'd be best friends, but we are. Just because you and your friend don't seem to have that much in common on the surface doesn't mean you can't be friends, I'm sure you still have a lot more in common than you're realizing. However, if she's changed into a person that you just don't like to be around, then ditch her, that's fine to.