[Judoh]

Your reason Q is identical to Ssol's theory where Kanon leaves at about the same time Erika does, Battler advances the game, and then after that Dlanor declares the rooms sealed. He did say there was a gap in time like that. However I think somebody said the solution wasn't that simple.

Here is a thought though.

Dlanor is presumably the person who applied the seals not Erika right? If Dlanor is represented by Kanon on the game board and is the person who seals the rooms than that would place Kanon outside the cousins room because it's impossible to seal himself inside the room when the seals are restricted to the outside.