I recommend a novel about a girl who was a bad student when she was a student. Later, she returned to her alma mater to be a teacher and taught in her brother's class.

I recommend the romantic youth-youth-school-based novel,"The Unique Tenderness of a Tough Girl: The Guardian Angel." The female protagonist of the novel was also a thoroughly bad student. However, after meeting the gentle and handsome male protagonist, she gradually transformed into a new self, and the male protagonist also became the female protagonist's exclusive guardian angel. This novel coincidentally matches your description of the female protagonist being a bad student at school and returning to school to be a teacher. It also includes the plot of returning to her brother's class. I hope you like this fairy's recommendation. Muah ~😗