I don't think she knows Iruma is a human, at least it wasn't shown to us yet.
I did say "people
usually don't". And her maternity dress
was different, this one is one of the casual dresses she was originally wearing at the beginning of the arc. Though, this one is significant, because of the cherry-looking decoration that led Henri to name her Merize.
I mean, true, it could be comfortable to sleep in, and she could've taken great care of it, yes. But have you heard of Occam's razor?
It
was confirmed that her hair color change was disguise magic. It obviously went away when she went back to the human world. The sequence just before her waking up could've been not her being transported, but, as i mentioned above, her thoughts or a dream. So we don't know when exactly magic worn off. If Nishi wanted to show that time had passed, you'd think there would be more change other than her hair color.
I never said that her home was created by demon magic, nor i mentioned anything about books, though?

Besides, Nishi haven't explained yet, how books came to be in Henri's collection (actually, she hasn't even confirmed that Merize was indeed the author of the books, though i wouldn't argue otherwise), but i'm pretty sure it happened after Merize was sent back to the human world.