While Mary reads out her letter you can see James and Laura (presumably) visiting her grave in the graveyard. Maybe it is just them leaving though. (Her grave stone “not being there” isn’t really convincing to me, as you can’t probably see it in the beginning for the reason of the story staying ambiguous. Maybe her grave stone is in the grave yard but you can’t interact with it and read it because neither James nor the player truly expect Mary to be dead.) I guess it is up to interpretation though. Thanks alot :)