If Kaori wasn't in the current state that she was, her reaction may have been marginally different. Because she was in the middle of this ability, however, she remained perfectly calm and went right back to trying to stab through the Nightmare in front of her, who just stood there and took it.
"I assume Lumina made you aware of the offer I proposed, right?" Niven asked as Kaori stabbed her swordstaff into the Nightmare.
Yes. Kaori replied in her thoughts, without taking her eyes off of the Nightmare.
"... And you're still going through with this? I wasn't aware you cared that little about your friends, or about your goddess."
Hm?