Its getting pretty hard to believe in any way that Hiroko is the "lesbian for the ages" that her bar friends talk her up to be, because at this point she's proved beyond a doubt that she's incapable of handling a woman. There is no way the Hiroko from chapter two, shown to be running through a blizzard in her undergarments, clutching some woman's bra as she makes her way to at least 2 more hookups, is the same character as this completely useless pile of fuck. And yeah, she knows Ayaka isn't straight either, and her excuse is ridiculously paper-thin. Seriously, Ayaka already knows it’s a lie and the barest investigation of asking literally anyone at that bar would prove it was a lie if she wasn't aware. Add to that how explicitly attracted Hiroko is or was, as you mentioned, and I think something is just not adding up.