The Coraline Door Theory

Was the door Coraline left through real or was she just going deeper into the other world? Most of us are familiar with the theory that Coraline may have never escaped the other world. This theory is primarily backed up by the cat disappearing and the garden at the end of the film. The cat vanishing was something he was able to do only in the other world and never did before she entered the door. And in the garden when panning out it looks like the Other Mother's face. Now while I'd love to unpack these two things I want to just focus on the door.