The incredible sadness of Shirley Jackson's novel We Have Always Lived in the Castle

Shirley Jackson's short novel We Have Always Lived in the Castle is another one of her creepy stories about outsiders - in this case two sisters, Mary Katherine (the narrator) and Constance, living with their elderly and frail uncle in an old mansion on the periphery of a small New England town - living in near isolation and near total alienation from the townspeople. We learn that Constance 6 years back had, for reasons not yet known (60 pp in) mixed arsenic with the sugar and essentially killed all the others in their family - parents, other sibs, maybe more? She was acquitted at trial but has never left the family house and property since. Mary K makes occasional forays into town for provisions, and is always met with hostility and cold stares, and even with bullying. This novel plays within the key of all of Jackson's fiction - stories not only of outsiders and isolates but stories of social ostracism (The Lottery being the prime example). What makes this novel, up to this point anyway, almost unbearably sad and poignant is what we've come to know in years since her death about Jackson's life; a recent bio (I read reviews but haven't read it) details the vengeful hostility of Jackson's Bennington neighbors - she didn't fit in, she was strange and artistic, an alcoholic, a Jew - and we can with no difficulty see how Mary Katherine is an avatar of Jackson herself, suffering teasing and bullying - and how frightening that is to know that your neighbors want you out of town when all you're trying to do is quietly live your life and get by.