Holy shit, what an incredibly good chapter.
It was almost entirely dialogue but it was essentially Mami's coming out chapter and was an incredibly in depth method of characterization as well as being one of the most "That's fucking real right there" manga chapters I've ever seen. An explanation and exploration of how people see women like her and how carefully she has to navigate relationships and friendships and everything in her social circle is put under a microscope. You also get some pretty wonderful bits of everything else: Masumi constantly telling Mami to keep it down in small bubbles, Masumi being incredibly defensive of her assumption about Mami and not backing down because of how mother hen-like she is over our hamster, Masumi's realization about how accurate Mami's discussion about Touma is in regard to her and Kuze (and that incredible pained expression), Kuze admitting she didn't like Mami cozying up to Taichi and her feeling bad about it because of everything Mami said being right, both of them reaffirming their like of each other and coming out strong for it, that dude from Mami's social circle calling her "buddy" and how important that is to her. Goddam. So much fucking happened this chapter.
And hell, this is an entire chapter after a "MISUNDERSTANDINGS!" cliffhanger where everyone sat down and talked about what happened and explained everything! That never happens! This manga is so fucking good.
And also no, gender discrimination is not just an excuse she's using; of course she wanted to get closer to Touma's friends so she could get closer to him. That's sorta what you do. A girl you like invites you to go with her friends and you say yes because you want to further your relationship with her. Like, no one enters into relationships altruistically. There's absolutely nothing wrong with her starting to hang out with Taichi so that it's less awkward when they're around each other with Touma and to figure out why him and Touma hanging out is so different than her and Touma hanging out. Mami isn't using him or anything close to that as we have just found out.