What should i Do?!To get her?

I don't know how you can get her to fall for you right away. Just remember it will take some time... If she has a obsession over this guy then see if that guy likes her back. If he doesn't then that's very good for you because then you will have a chance. Just get to know her, become her friend, get close to her and then she might realize that you are the one. :) <3