...this manga is very neurodivergent in the best way.
"Oh, you're a monster, but you don't make me uncomfortable. Other people make me uncomfortable, but non-humans don't." Fucky. I love it.
Itou notes in chapter 8 that she disliked the teacher while he was alive. "His eyes always looked like he was
appraising something in us. I hated those eyes." Itou also immediately connects the teacher's gaze to the scene he witnessed in the storage shed: "I still don't know what he did to Takahashi-san behind these doors." And now in chapter 9, before she tells the new monster that she is not uncomfortable, she says "You aren't Mr. Niehara" instead of just "you aren't human" or something similar.
That's why I think in chapter 9 by "uncomfortable" she does not only mean anxiety that an awkward girl might feel around every human, but a more specific sense of wrongness caused by the teacher (who might have been a sexual predator) specifically. Though in chapter 9 she also clarifies that the teacher did not necessarily (or only) appraise the girls' bodies, but whether they're "normal good girls", and Itou failed in his eyes in this aspect. (It's pretty likely that Takahashi was targeted by the teacher because she came across as a "normal good girl".)
While Itou might have some kind of neurodivergence going on, I think it's pretty 'normal' to be creeped out by a person in this way, and her opinion on the teacher does not necessarily reflect how she feels about other humans.