Bisexuality Support Group
Bisexuality is a sexual orientation which refers to the aesthetic, romantic, and/or sexual attraction of individuals to other individuals of both their own and the opposite gender or sex. Most bisexuals are not equally attracted to men and women, and may even shift between states of finding either sex exclusively attractive over the course of time.
It seems to me that she is probably either making fun of you or trying to get a reaction out of you for some reason. Has she ever mentioned in the past that she was bi/lesbian/etc.? She might be genuinely interested in being more than friends, but if she hasn't mentioned it before, then chances are she's just toying with you.