life is full of unpredictability and surprises, the deed has been done , the mistake has been made.
Let Your mum focus on cautioning her against make another mistake. But from another point of view, i somehow blame you for not reporting her to your elderly ones who would have given her a more severe punishment . The moment you noticed that what your are saying is actually falling on a deaf year, the next step should have been a more disciplined action. The bible says , " spare the rod and spoil the child" .
Life goes on, i pray and hope she does not repeat mistake again.