The picture above was from the intro, where they talked about how this all began.
Honestly, I would prefer after the sex events. She would turned to the way like this rather than the whole slutty behavior thing. I rather see her as the sex craved thing but still maintain her priestess self and guilt ridden.
The now Cecille feels a 180 compared to her past self. Like I get it. That's the point of the game but feels way too endearing and annoying.
Just look at Sera. Even after the sex events. She still maintains her true self and not slutty. That's why she's the best girl along side Vi.