I used to think "this is a bad manga, but I still like it." After this chapter..I just don't know anymore. It might actually be more well written than I give it credit. Or I might be reading too much into it.
This looks like some kind of subversion of the yandere trope. Usually we have a plot with a innocent girl, in innocent moments that turns out to be a psychopath. Here we have a girl we believe is a psychopath, but that the more we learned about it, the more we realize how wrong we are. We though she killed her aunt, turns out her aunt is alive. We thought she wanted to off her friend, turns out she really just wanted to be her friend. Not to be rejected.
The point where she asks Shio what a friend is and both say they don't know it is pretty telling. Those are two lonely girls that were rejected by people around them. Sato in particular was rejected because she was "weird". Can we blame the kids who made her that lonely? We can't. We were sure she was a murder and crazy. We were sure she killed her aunt, and that turned out to be wrong. We were sure she would try to kill Shouko, but at the end she truly just wanted to be her friend. Sato is surrounded by awful people. Shouko is one of the few decent people around her, and Sato always treated her fair. But we made the same assumption the kids on her childhood did.
Again, I might be wrong. Who knows. But if I'm not, that's a pretty interesting approach to the genre. I'm curious about how the next chapters will go.