Most Helpful Guy
Honestly, this is pretty confusing. Perhaps she is saying that because she recently broke up, and you are the rebound guy, in which case sever all ties with her. She doesn't respect you or your feelings if that is the case.
She could also have a friend of hers that is single and wants to match her with you, although she should have lead with that when she asked if you were single.
Those are the only reasonable explanations I can think of, but the only way to know for sure is to ask her why she is asking of you are single, if she is already in a relationship.