If it is an ongoing problem, maybe your parents should take her to a child psychiatrist.
Maybe this is an episode, and if so, surely the psychiatrist will catch that and there will be not much to worry about. If it isn't an episode, it's something to pay serious attention to to make sure it doesn't escalate.
Adult problems can find their roots in child problems. I know an adult woman who, as a child, had untreated psychological problems and she developed Borderline Personality Disorder later in life.
There may of course be many factors at work here, but I wouldn't rule anything out -- and so professional help seems in order.