You need a reality check, A bi female will always be bi no matter who they are with. It is my experiance that there are always two types of bi females those that prefer to spend most of their time with men and choose to sleep with women when they feel like it and those that spend most of their time with women and sleep with men when they feel like it. If you felt that you "would have straightened them out" had they been with you then you are sadly mistaken. My psyco analisis of the situation would be less of the fact that you would have straightened her out and more of the fact that she was just not really into you in that way, In other words she was not sexually atttracted to you otherwise she would have sealed the deal.
Britexpat is right you also confuse bi and lesbian a lesbian is a female who is attracted to females only so if she was a lesbian then there was no attraction at all on her part towards you a bi sexual is some one who is attracted to both sexes be it a male or female also affectionatly known as a "double adaptor' or "fence sitter"