Can confirm: I encountered this issue. I assume since Tulpy is missing an item slot, her slot is always Slot 1, which is the item you always carry keys with you.
To make a reference: Slot 1 is mainly Keys, your Right hand. Slot 2 is mainly other items like Apples or Papers, your left hand. And Slot 3 is reserved for Predators where you select it to either devour students or rub your belly.
Since Tulpy can only have 1 item slot (Right Hand), Tulpy can carry many different item types one at a time. Thus, the game ONLY detects whether if the player has a book on the Left Hand, which is non-existent for Tulpy’s case.