It's part of the world's "mechanic", it's normal, and it's how the world works, as shown in the intro.
And listening to the story, Emily and Rose did both know about her and that she was living there.
Why would they?
As I said, they both knew that she was hiding in the attic, and the master-tamer thing is part of the world, so it’s not something that’s a rare and weird occurrence.
I feel like something is getting lost in translation, because I’ve said this multiple times now, and I know it’s also said in the game.