i don't see the direct relationship to the tragedy. Even she knew 刘 is a 损友, or just a passerby, if 刘 was in danger, she still should help. The real question is learning how to help and how to assess the situation. She was brave, but in this case obviously brave wasn't enough...
She and Liu should avoid this emotionally unstable guy when they felt the potential danger, don't let him even have any chance to be near.
If they can't avoid, she shouldn't let herself in that position without any weapon or ways to backout(like a window, or a door), she needed some very basic training of self defense. If one can't defense self, how can one save others? She didn't have any physical and mentle skills to help her "friend", the best way should be running away to call for help.
