It sounds like she has a lot of anger built up and doesn't know what else to do with it. While I would make an appointment for her to see a psychologist asap, I would also reassure her that we all get angry (mad) and feel like we might want to "kill" someone or stop something or someone for something that happened, but that we can't act on those feelings. Try to comfort her and allow her to express her feelings in a better way, if not by talking, then maybe by coloring or finger painting (black and or red colors work well here.)

I'm sorry that something ..or a conglomeration of things... has affected her so strongly.