The flashbacks were more of a child through a tantrum at first glance, here she just straight up fisticuff'ed a whole classroom.
But I mean, she has beaten up quite a few ducks there (considering she was youngest in the convent at that point, with Star being six years older than her, she probably wouldn't stand much chance against people in convent).
Edit: Well, after post #9779035 I'm taking back that later part. It seems that she was really ready to go against anybody, regardless of their age.