You know what they say, hell hath no fury like a scorned women. Especially a scorned women that came crawling back completely vulnerable looking to find closure by opening her legs. That doesn't excuse this girl's homophobic messages or her general misconceptions about simultaneously being bisexual and monogamous, but it does explain why she was so quick to exhibit it on someone that seemed pretty mild mannered throughout the entire interaction.
I actually don't even think this woman has problem with the gay community, I think she just dug into her bag of weapons looking for whatever words would cut the deepest. Rationality and acceptance be damned when a 21 year old girl is just trying to reciprocate the pain of abject rejection on the person who caused her that pain. The fact of the matter is that women are mental terrorists that will say anything to make you question your self worth even if all you've done is indirectly and innocently make them question theirs. Maybe this girl is living in a previous era with her views on homosexuality. However, I have reason to believe that she's just a lonesome chick looking for some decent dick that felt insecure because she put herself out there on the feeblest of limbs and didn't know how to respond when it went crashing down to the ground under the non-existent weight problem that she continually claims she's in the process of solving. There's just no doubt she was on the precipice of a full blown hysterics when she tried to take a trip down the old roster to provide a quick fix for her loneliness and this guy incidentally pushed her over that edge. Unfortunately he provided her with the ammo when he did, and she didn't hesitate to fire off a barrage of discriminatory insults that were better left in a previous decade.