Lets face reality, as a parent myself I am responsible for my children until they are on their own. Then you can only hope you taught them well. Parents are responsible for their children. A teen is a child. If your teen is an idiot you are to blame. You did not do your job, which is to teach them the things they need to know about life and the world. Its not about if they are doing things you are unaware of. Its about if you taught them that there are consequences for their actions, respect others, and established a moral basis for them to live by. Or if you taught them that they are the most important person in the world, and that they should have all the latest and greatest even if they havent earned it. I always blame the parents when children are arses. I also credit the parents when children are good. You see children dont know anything but what they are taught. This young girl was not taught to respect others, society, and life. She was also not taught that she has a responsibility to society in general. And yes we have responsibilities to the society in which we live. Them main one is to not endanger the lives of the others around you. Then to respect their person and property. Evem if you dont know them. Especially if you dont know them.
This young girl was not taught this simple value and was acting totally narsissistic.

I have no faith in human perfectability. I think that human exertion will have no appreciable effect upon humanity. Man is now only more active - not more happy - nor more wise, than he was 6000 years ago. Edgar Allan Poe