On the surface it seems like Rabbi Yoffe’s statement is the most accurate answer. That said, as this was written from the perspective of only one party, there’s more to the story than meets the eye.
I read the full question and it sounded like the girl was a bully back in high school, so while the girl may have apologized to the teacher, what about her other victims? A good teacher would guide her/his student that while they can be mochel on their honor, they can’t be mochel on sonmeone else’s, and the girl must be mefayes her friends who were harmed by her. The bully refused to do this. From the teacher’s line of “I know, what I know” that she feels the baalas middos raos would be a disaster as a wife and a poor excuse for a mother.
Let bullies who aren’t mefayes the ones they harmed hair turn white before they can get married.