I think it's weird that it took so long for Denji to just...attack the devil.
It's funny, I don't think anyone on the squad has any idea how strong Denji is, because none of them have actually SEEN the Chainsaw Man before. Power and maybe Aki saw the half-ass version with the little chainsaw sticking out of his head, but neither have seen him go full Devil yet.
I don't see how she's crazy. She's responding to an otherworldly horror with panicked terror. That's a pretty standard response I say.
Devils feed on fear. When she said the devils fear the crazy hunters, I assume she means crazy like Denji, i.e. will just fearlessly run in slashing, because he has no sense of self-preservation.