@NIB
This chapter left me with a bad taste in my mouth too, the first time. Whenever you're not sure who's telling the truth, it can be frustrating. Yadorigi's internal monologue confirms that, at the very least, she isn't aware she is possessed (which hasn't been a thing so far).
As for when the alleged Kirita possession happened, it could be when Yadorigi thinks, or it could be after that. Either way, it's confusing.
It also sucks because possession has been literally akin to character death in this series, so revealing characters to be possessed is essentially revealing them to be dead.
One thing that might make things less confusing, is the detail Shino gave in her internal monologue while trying to possess Rokurou. She said that normally they destroy the person's soul before taking over, but it was also possible for them to take control while the person's consciousness was still alive. Surely that method is unreliable or they'd never bother with the paintings at all, so I'm certain Takoha's ability to save people from that first step of soul-death is still really powerful.