I also didn't get into Shirley Jackson's books until way late in the game! I really like horror like "We have always lived in the castle"

I agree that they added a bit more flair to the movie with more witchcraft but honestly shirley jackson's writing is so subtle, there's probably a lot that they couldn't convey in a movie. I saw the end when she says she's happy as her being finally free..but I could also see in the movie if they were just showing some kind of hidden trauma that's still there.