Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.
Not without a lot more information. Even THEN, I am no expert. A mental health professional (FULLY qualified) would give you better answers than I ever could.
I can (probably) waste some of your time with the following:
What is her diagnosis?
What is her age?
Is she in school? If yes, is it a 'special needs' school?
Is she aware that assault and battery is a crime .. even by the mentally ill?
You can discuss this with a layman .. with limited results or with a professional and find out what is best for all involved. I recommend the professional.
Sounds like this behavior has been present for a good long time, and its just escalating. She's doing it because she can.
I would phone her former therapist for suggestions, and options. This can't be allowed to continue. It must stop now, otherwise it will get even worse.
Good luck.