Can a girl like another guy even when she has a boyfriend?

Is it possible for a girl to like another guy even when she has a boyfriend? This girl I've liked for a while always flirted with me in class she definately likes me I think I know the line between just flirtatious and actually liking someone, she comments on my FB statuses all the time but she has a boyfriend from another school where in grade 11, could she like me despite her boyfriend??