Do you think Rachel would or has struggled with her sexuality? If we read her friendships with Quinn and Santana, or example, as driven in part by some level of romantic or sexual attraction, do you think this would be challenging for Rachel to parse, or a point of tension? Or does she just never explore it in canon because the opportunity is never there?
Imma put canon aside for a second be she's simply just not canonically queer but it's SUPER fun to think about a better show where she was so, yeah. Rachel's bi as far as my version of Glee is concerned.
In terms of how I see that going down, two ways. One more comedic and one more dramatic, depending on which side of the bed Glee would have woken up that morning. The more comedic version would have her behave similarly to how she did in Blame It On the Alcohol. That is, she'd view newfound feelings of queerness as a great opportunity for artistic expansion and would be a little over the top and silly about it. So, say, Rachel realizes, preferably when she isn't currently dating Finn, that oh shit, maybe she's attracted to Quinn, too. And because she's Rachel she'd go all in and be very grand gesture about it because yolo and push! Push your feelings away, they're that big! She wouldn't feel conflicted about the queerness of it all for long because, given her dads, she's always always been comfortable thinking outside of heteronormativity. If anything, she's a little relieved and very pretentious about it because now she's not only an ally but bisexual herself! And she does not shut up about it for a while. Very out and proud, but also treating it as a very natural thing because to her it is. Also idk why I used Faberry in this hypothetical when I've actually read a REALLY good Pezberry fic that handles Rachel in a similar way to what I would imagine. Please read that fic, I'm still hoping it will get finished one day.
The more dramatic approach would be to have Rachel struggle a little bit with the realization. And that would be understandable as the two most obvious candidates for her to realize her queerness with are Quinn and Santana, both tumultuous and complicated relationships. I kinda feel like it being Quinntana would be more of a point of tension for Rachel than just bisexuality itself. Because, say, in a version of Glee where Rachel develops feelings for Mercedes I really don't see those feelings posing a challenge, as such. Not the queer aspect of it. Rachel Berry is a lot of things and a staunch ally from day one is one of them, even if she is misguided on occasion. So realizing that she herself is queer wouldn't cause a crisis of identity nearly as much as it would for other chs (cough Quinn cough).
In terms of Faberry and/or Pezberry, however, there's angst potential. Say, Rachel realizes just as the Pezberry feud is happening that oh, no! Not only is Santana hot, which is something Rachel's always known, but she's hot in a way Rachel's very attracted to and now that they're fighting she realizes she's missing Santana as more than a friend. And that would be challenging to parse because I think she'd feel like she's not supposed to like Santana and would somehow project that onto the whole idea of Sapphic tendencies. And it would make her reevaluate the complex dynamic she had with Quinn, too. Additionally, this coming just after Finn's passing, too, would make Rachel feel like she just doesn't know herself and what she wants. So I think grappling with her own queer identity would make her spiral in that way but even in such a scenario the root cause of any tension wouldn't actually be her sexuality. It's just the specific circumstances, you know. Why her, and all that.
That said I don't think that it would always cause Rachel to spiral a bit, like I said this is the more dramatic version of events. I think, ultimately, that I just have to approach this as a matter of what could have happened in an alternate timeline because as fruity as I read Faberry and Pezberry, any sort of romantic and/or sexual feelings on Rachel's part are not canon. So like, that's why it's never explored in canon. But even if we don't totally rewrite things and instead just pretend those feelings were there and Rachel grappled with them at some point, I think the queerness of it all still wouldn't be a big deal to her. If Rachel were to realize in retrospect that at least some of her relationship to Quinn and Santana was motivated by those sexual/romantic feelings she'd quickly come to terms with bisexuality and just go "oh okay, cool!" Given that those feelings were in the past and/or not possible to act on, such as her looking back on it when married to Jesse.
So I hope that answers your question; this is fun for me to think about because the Fapezberry triangle is delicious. Even though we don't have canon queer Rachel, adding her to the mix just makes things even more interesting.