@drmkultra well it's funny, but for some people they don't like that she's making Komi-san a little uncomfortable with her yandere-ness or don't like how she's kind of a jerk to other people other than Komi-san.
@Kutabarie @freezeman
Hey a passing re-reader here. You are not alone on that regard, a good portion of the fandom hate her as well though some people think its attractive. She will become irrelevant later on and rarely appear except on few chapters, hopefully the fluff in the series will outweigh it.
Personally i also don't like yamai in the early chapters as well. But if you keep reading till it reach second year, you are in for a surprise development.