Sounds noble, but this actually not the right thing to do. I’ve seen this scenario played out as an ethical dilemma before. The appropriate action in all situations is to always report to authority. Whether it’s about your coworker (talk to your boss), a thief (call the cops), or your child’s teacher ( report to her principle). One explanation for this is this will often times backfire, and there is nothing you can do about it. Another is, you do not have any authority over this teacher. Finally, you have no report or skill in managing the outcome of the scenario. The teacher may become hostile may also feel threatened, not exactly the outcome you’d be expecting but it is the often outcome. Point is this teacher has an authority figure over her for a reason. Don’t over step that boundary. Report issue to the principle.