For the big brains up here in the comments, trauma doesn't have to be directly proportional to the actions that caused it, much the same with guilt. When she bullied Ruri, although it wasn't intentional, it targeted something she seemed to be deeply insecure about; likewise, depression can distort your memories or the gravity of them, so I don't think it's weird at all for the MC to be the way she is. Not to mention that these are all kids, everything seems as it was yesterday and they don't deal with shit perfectly. Hell, as if adults can.
While I like a Silent Voice much more, saying that the reaction here was forced or felt off seems like a baseless critique to me.