How do i get this girl i like that has a boyfriend to like me?

Im in her homeroom cl and her bf goes to a different school. We text alot almost everyday. I cant ask her on a date or anything because i cant drive. Also theres a school dance coming up. We made a plan that if a guy thats obsessed with her asks her to dance shell say shes dancing with me. Should i follow thru? She knows that i like somebody and she keeps on trying to figure out who it is. Im too scared to tell her