This manga is so confusing. I expected quite a lot from this artist. Somewhat disappointed. Till the end I couldn't tell if she was into the other girl or not.
This. Only by the end of it, my impression was that she was not into the other girl. She does not contemplate being attracted to girls, is not shown as such in any way, and does not show any signs of being interested in Nozomi specifically, in a romantic and/or sexual way. To me, it literally looked she raped her out of frustration over herself 'stepping into adulthood', so to say, while her best friend showed zero interest in these things, and thus she feared they will grow apart, someone will be "left behind" and whatnot. This fear and frustration leading her to basically assault Nozomi.
In fact, all her thoughts on the matter seem mostly het. She is obsessed with the image of having a boyfriend (even asking Nozomi this, right before the rape, like, not a 'lover', a 'romantic interest', a 'girlfriend', 'me', no, she seems single-mindedly obsessed with boyfriends), considers her first sexual experience as a sort of social triumph, despite it being painful, and at no point does she think of it as a mistake, nor does she expand her list to include girls, or even contemplates such a thing. She also genuinely seems to think "it did not count" between them. Even when Nozomi manages to convey it does, in point of fact, count, her reaction was a warped feeling of happiness that her friend is no longer a virgin, zero thoughts spared to the fact she just had sex with another girl. This page is literally the only thing that stood out to me as 'she might be into her', but it was just not enough to cut it for me.
And as far as Nozomi goes, she too is not shown to be interested in girls, or anyone, for that matter, and is basically overpowered (though it seems more psychological than physical) into submission here. Sure, she thinks sex between girls is just as valid as the het version, but that does not necessarily mean she is into girls herself.