While the other family didn't have to kill Sayuri (just overpower her), it seemed she really wanted to hurt them and they reacted in self-defense. Mostly the father's fault for being the one to actually choke her.
This would make a good drama and it's an interesting take where the ghost actually gets punished for hurting so many people that weren't even involved.
Sayuri was kind of an asshole in life and so stayed one in death.
Pretty tragic all-around that there's no happy end for the ones that died (they get their own justice on Sayuri and that's it), but the main trio get to live the rest of their lives to the fullest.
Got pretty heartfelt then.
EDIT: Wow, just saw that a film version is opening in August. Definitely interested.