it sounds as if her grief, for your brother, is coming out in acting out and anger.

has she talked about losing him at all? do you talk about it, as a family? or one on one?

if she could get some help, a therapist, she could talk to someone objective. in the meantime, approach it, in your mind, from that point, that she may be so grief=stricken that she knows no other way to express herself........

good luck, xoxox pat