Indeed it wasn't her fault, but I think this is the first time Kyoukai has "failed" in accomplishing something on the battlefield, and the first time she's been scolded by Shin for it. New territory for both of them.
Look at that parallel yet again. First Shin failed to save Seikyou at Tonryuu, now it's Kyou Kai who failed to save Ten from Junsou - and it's as @pdonk said, this being new, but the second time they've argued this fiercely since Kyou Kai's assassination attempt on Sei. Interesting.