Here we go again.....

My oldest daughter, B. is in a bad place, again. She is posting on her webpage about wanting to cut herself. Wanting to go to sleep and never get up. She won't talk to me. Her outward demeanor is hostile. Angry. Or alternatively, completely unresponsive. She doesn't try to fight it. She won't let anyone help her and I don't know what to do. She scares me when she is like this. I never know if she is just venting, or when/if it will go beyond words to action. I don't see any signs of mania- only depression. God I hate this. Why can't I help my child? Why won't she LET me? Doesn't she want to be happy... to somehow move beyond the demons that haunt her?