I would think anyone could "do it" as it were. Some sort of masking spell or enchantment on the home.
I just don't think it's anything that is special about Joan or her aura that is allowing her to stay "hidden"
They don't know who she is simply because they don't know who she is, and the Gendarme don't see her in
the house because there's some sort of enchantment on the house that hides her presence, which was likely set up originally to hide her from the media and paparazzi due to Germain's fame.