Why is she so obsessed with me?

This girl in my higjschool class that is totally obsessed with me she follows me stares at me she touches my desk.when I get up to get sime supplies for class she gets up. She even has our future planed out. I soo dont like her but I like her best friend because she doesnt care about me or stare at my butt I use to sit next to her and dream about her all day. She is my type she isnt obsessed with me when she isnt looking I stare at her even when we are watching a movie in class and she is sleep I go sit next to her. I really want to talk to her but everytime she is with her crazy friend. What should I do?