I agree with Bein Hasedorim. I also believe you should tread carefully,but try to get a feel for whether or not this girl would be interested (she might not be, even without the issue of her girlfriend, as a factor). If she IS interested, she might want to talk to her friend about it. I hope this works out they way that will bring you simcha and not cause pain to anyone else.
Who knows if your former engagement was specifically designed to ensure that you meet the other girl?