Remember how she was given a book but couldn't remember who gave it or why it was given to her? I'm assuming her blood is special and different (perhaps like those fae folk stories of fae who seduce humans, her mom was a supernatural being) and just like the giver of the book was able to elude herself from everyone's memory, so were the maids - everyone except Cecile, of course. I don't think they didn't exist or weren't human in form, but can rather control and manipulate memories.
Remember how she was given a book but couldn't remember who gave it or why it was given to her? I'm assuming her blood is special and different (perhaps like those fae folk stories of fae who seduce humans, her mom was a supernatural being) and just like the giver of the book was able to elude herself from everyone's memory, so were the maids - everyone except Cecile, of course. I don't think they didn't exist or weren't human in form, but can rather control and manipulate memories.