"She's one of the only people who isn't gay because she had an immunity to the potion and by now, she gets as much heterophobia as some people have had homophobia."
I don't think it would be the same at all. If the potion had been released several hundred years ago, sure. But everyone has grown up with hetersexuality as the norm, they won't reverse their views overnight. Most homophobes would still
be homophobic, and might either kill themselves, search for a cure, be celibate, or stay with a heterosexual lifestyle despite not enjoying it as much anymore. The people who were supportive of gay rights would be supportive of the heterosexual minority as well. Only a very small number of extremists would treat heterosexuality as a bad thing, basically the same people who did before (eg radical feminists, gay misogynists, etc).
Over tme, a bunch of people would start rethinking their views. Some might stick with their original view but flesh it out a bit differently (eg 'men are evil and we should all be lesbians' shifting to 'men are evil, let's persecute the men'). Some might become more tolerant (eg 'I always thought it was a choice but now I understand that it's really not'). Some might become less tolerant (eg 'I thought being gay was just as good as being straight, but now it's clear to me that an all-gay society really doesn't work'). Counselors would be in big demand, meanwhile they'd also be sorting out their own issues.
Just out of curiosity, what happens to asexuals? Would they gain a sexuality? Or would they be immune?
If I'm asking for advice on a story idea, don't tell me it can't be done.