Kurumi has been pretty consistent that her main tactics for dealing with conflicts is repressing her emotions and doing what other people want. She is learning to advocate for her needs and desires more, but it's still difficult and often more all or nothing for her. Right now she is very scared, while Kokoro is hard mode for applying this skill at the best of times. We also see that, despite everything, she still thought of Kokoro as a friend whose relationship she valued. It is Kokoro herself who rejected that this chapter.
A lot of people were wanting or expecting something different in terms of Kurumi's behavior. I find this realistic, as people don't change that quickly in general. If we compare to her behavior in previous arcs, Kurumi has been more bold and self assured, but this doesn't mean she is yet a character we could describe as bold or self assured in absolute terms.
Attacking Naoi would likely enough to get Kurumi out of her passivity and trigger the "all" angry Kurumi outburst, except Kurumi just passed out. This is a good setup for Naoi to do something knightly to save Kurumi and have Kurumi wake up next to Naoi some place safer. Though the author is good at surprise developments that defy expectations, so who knows.
