I dig the shit out of the whole "people who look a certain way doesn't mean they are a certain way" motif of this series.
We obviously have the Ice Princess who has the blank, passive "resting bitch face" vibe that the MC had to sort through and get used to -- but a new side-character who has an actively aggressive expression as her "default", who gets ostracized because the others are afraid of her, is a fantastic addition that helps our Ice Princess also further work through her own situation, while using her skills and experience to help someone else out at the start of things.
Hopefully the next chapter is Mizudori helping her show the rest of the class that it's merely her face, and that she's not angry or standoffish or rude or mean, and they can acclimate and learn the subtleties, and she can build confidence and make new friends right away.