In the moment, with everyone and everthing going on around her, I doubt she was thinking rationally or even knew that torching a car would be a long prison sentence. (if someone asked me before reading this article, I would have assumed a large fine + some community service maybe; then again I am not American so I have no idea how sentences compare).
That phenomena is why I don't participate in this sort of events. The best way to avoid getting swept up in a mob mentality is to avoid the mob in the first place.