I'm going to try to preempt those people who will whine about her "protecting" a person who was clearly attacking her...
It is easy to allow someone to be destroyed. It is easy to destroy someone. It is easy to cause someone to destroy themselves. (etc). What is difficult is to change someone.
By preventing the teacher from being isolated she prevented someone from having something similar to what happened to her (bar the obvious, execution) happen to them AND potentially changed (or started the change) that individual for the better.