I don't understand this girl please help?

There is this girl I work with and I really do like her a lot. The thing is, she used to have a thing for my friend(who works with us aswell). She still chats with him, and she even sat on his lap today. I asked her out to a movie a week ago and she said okay, then she suggested that he come along too. She claims that she is over him. A few days ago at this party, her friend(she was drunk) told me that this girl really does like me, but she told her not to tell me about it. If she does like me, why is she playing these games with me? Why does she flirt with my friend? Is she really into me or more into him. I totally ignored her today, and I could tell by her face that she was sad. What should I do? Do you think this girl is worth the heartache or should I just continue to ignore her?