Mitsuki is definitely super cool in this chapter and I'm glad she is able to show her real self in public, but I'm a bit upset as well that she doesn't let Aya knows that she's fine. Aya have probably been worried sick, to the point were she wonder if she did well getting angry and yet she is being completely let down by Mitsuki.
It's been like that for quite some time already. Aya seems more like a supporting character rather that being part of the main cast and the last panel makes me think she feels that way...
I get what you mean, though I also get what the author is going for with this whole arc. You know the saying that before you start dating someone, you should accept and love yourself and be happy with yourself as you are ? Because otherwise, the relationship cannot be built on steady ground and if you're not happy with yourself, then the burden of making you happy falls on your partner, meaning that you become dependant on them, which isn't healthy.
As I see it, until now, Aya has been much further along on this path of self-acceptance than Mitsuki. She knows who she is and, thanks to Mitsuki, the only part of herself that she didn't feel confident about showing in public (her love for rock music) has become something that Aya feels more comfortable about, including in sharing it with her other friends. Mitsuki, on the other hand, while she had become a bit more confident in herself and open to others thanks to Aya, was still doubting and hiding herself quite a lot, as she wasn't fully comfortable in owning up to who she is in public. This whole arc about Mitsuki making music for Aya, letting her listen to it and even playing in public was supposed to make her grow into the person she needs to be to be happy with herself and able to be in a healthy relationship with Aya, where they wouldn't depend on each other to be confident and happy and the happiness they bring each other is a very special bonus, but not the only happiness they can have.
I'm not sure if that makes much sense, I'm typing this quickly, but basically I think Mitsuki had a lot of growing to do before she could become a person who could actually stand by Aya's side as her lover and not second-guess herself every two seconds, and she had to work for that growth on her own (though Aya's support is part of what made it possible). I'm sure she had a lot of thinking to do in the week between the two eps and she knew she had to do it alone (because I think that, if she talked to Aya, Aya would have told her that she was fine just the way she was and she shouldn't push herself too hard, so Mitsuki's growth might have been halted by this).
