I was wondering if the topic of Borderline Personality Disorder has ever come up in terms of either being diagnosed or eliminated as a diagnosis. As soon as you said she was cutting, I wondered if BPD had ever been considered? Here's a little bit I cut and pasted from a BPD website:
"While a person with depression or bipolar disorder typically endures the same mood for weeks, a person with BPD may experience intense bouts of anger, depression, and anxiety that may last only hours, or at most a day.5 These may be associated with episodes of impulsive aggression, self-injury, and drug or alcohol abuse. Distortions in cognition and sense of self can lead to frequent changes in long-term goals, career plans, jobs, friendships, gender identity, and values. Sometimes people with BPD view themselves as fundamentally bad, or unworthy. They may feel unfairly misunderstood or mistreated, bored, empty, and have little idea who they are. Such symptoms are most acute when people with BPD feel isolated and lacking in social support, and may result in frantic efforts to avoid being alone.
People with BPD often have highly unstable patterns of social relationships. While they can develop intense but stormy attachments, their attitudes towards family, friends, and loved ones may suddenly shift from idealization (great admiration and love) to devaluation (intense anger and dislike)."
http://www.nimh.nih.gov/publicat/bpd.cfm