I definitely thought Kotaki would just be a third monster. Or, somehow, N-sensei in disguise. I guess both of those are technically still in play until we see the two in the same panel together on this trip, or we see Kotaki eat someone or something.
But either way, her clocking "a monster" seems like it's setting up her cottoning on to Takahashi, but it could easily be she's clocked monster-sensei, as well. Time will tell, etc.
Another wrinkle for Itou & Takahashi, though. Especially Takahashi, who now has both another person on her literal tail, though hopefully not another romance rival (or "vying for eating Itou" rival, I guess)
Thanks for the TL.