Need some girl help... girls only..?

okk heres how it is theres this girl i like and i stay the night at her house like all the time, yes im friends with her brothers. she just broke up with her boyfriend like 3days ago, she said that she would date me if i didnt act like a bro. how can i get her to like me.? how do i not seem like a bro? etc. i just need help please im going to see her sat. night and prob. stay there... need help please..