***SPOILERS***
From my understanding of the secret ending, Cece just wrote down the text on the door as a joke, a prank, but then with the professor appearing and confirming he needs one of them to die, that prank became a reality.
With that said,I don't believe the secret ending is ruining Cece's character or anything, it just gave a better reason as to why for this last soul to die and only for that last soul it needed a killing game :p