Don't think I've seen that. Or read it? Sorry, not entirely sure what that is in general.
The letter Carstairs left, even if that was him leaving it, said his third did put a curse on him/the house. Somehow I can see it being the opposite of that though - he doing something to her and this being a by product of it.
There's been a lot of rooms coming out of rooms, for all we know maybe she was entombed in something similar?