This is the way of stops in a road-trip post-apocalypse: it's just another flavor of fucked up waiting for you. I really don't know what to think of it since the Grandma gets nothing at this, concretely, but Hirukos are too much of an unknown to be left idle next to an entire family.
Though, I want to believe her, that the hiruko was there without problem for centuries, or else her family wouldn't have that tradition and history backing it up. So the facility may have found a way to reproduce a natural phenomenon.