How do I deal with a copycat friend?

Don't get me wrong, I love my best friend but she can be a bit of a copycat sometimes. In 5th grade she used to copy my outfits everyday, and it took her a while to grow out of. Now she just seems to copy my music taste. If I like a song, she buys it on iTunes. She always used to say that she hated Miranda Cosgrove but then I told her I liked her music and then she started listening to it. At her house she asked all the songs I liked and bought them all on iTunes! It seems like she doesn't have her own taste. And like I said I love her but I just want to know what I can do because I don't feel like I can be myself now!