I know we're all gonna jump to the pessimistic takes, this was a potentially risky move for Mitsuki: Aya might be disappointed or even angry, she might get in a fight with Chizuru, Chizuru hates the concert, etc etc. There are so many ways this can go wrong, but as an alternative, let me suggest a more optimistic possibility:
Aya goes to the concert with her friend, they actually have a blast, become closer friends, Chizuru learns to appreciate Aya's interest in western music, even if she doesn't really share it. Aya feels seen and validated, and when it comes to Mitsuki, recognizes the gesture for what it was and loves Mitsuki even more, but still sour she got stood up for her concert date she demands a date-date as compensation for the fakeout.