Don't get caught up in the mind games. If she has a boyfriend then she's either just fucking with you or you're reading in to it too much. I'd say forget about her. The benefit of this strategy is it saves you a lot of energy, and if she is trying the whole 'hard to get' bullshit then it will only draw her in quicker. Nothing gets a girl's motor running faster than being ignored.

No matter what her intentions, the worst thing you could do is give her the satisfaction of a reaction.