Seeking the sources for a story

I have heard the following story, from a source I do not consider very reliable. Are there sources for this story? A Buddhist nun has killed a bandit deliberately (not in an act of self-defense, but to generally stop him from being a bandit and possibly killing people). She has told this to her spiritual teacher (possibly, the story of one of the previous lives of the Buddha in which he has killed a person deliberately, came to her mind). However, her spiritual master told her that she has committed a major offense, and that she is no longer a nun. He said that in contrast to the Buddha in his previous lives, she A) did not try to change that person for the better B) did not consider the possibility of lower rebirths, when killing. Note : The story is more probably to come from the Mahayana (due to the reference to the Bodhisattva killing a person)