The key’s smaller than most of the others on the bunch, but you can pick it out easily because it is always slick with fresh blood. Some magic keeps it that way, never dripping, never drying, never rubbing off onto the other keys or onto your fingers. Not until you choose that one, put it in the lock, open the door.
I know she’s looked at it. They all do. Perfectly reasonable, a bit of curiosity. It’s only to be expected when something so mysterious is forbidden to you. And there’s always a chance everything’s going to work out this time – if all she does is look.