Do you still have any contact with this girl? Cause being friends with her and showing that you can be trusted can help you. In either case it may please you a little that you at least make her feel like there is always someone there for her. I have had female friends whom have claimed to be lesbians because males only have hurt them, and the whole breed makes them reimagine what made them feel that way. Kinda like you and lesbians...
However, and this is a MAJOR however. Trying that would possibly make them angry if they start thinking your only doing it because you want them to agree with you. But this would not be a problem if you truely like the girl. It may also hurt you if she truely are a lesbian. My feelings about it tho is that love is not bound to the sex of the creature.