Clinical negligence-help?

My sister was severly depressed and slit her wrist a few months ago in a failed suicide attempt. The hospital offered her no counselling and after stitching her up, badly, sent her away. This has left her in possibly a worse mental state than she already was and has taken a couple of overdoses since. She is nw under counselling, paid for by our family. The scar she has been left with is incredibly large and angry and she is increasingly paranoid. She has also been left with slight nerve damage after being told at the hospital that it was a "superficial" wound. My boyfriend mentioned that she may be able to sue them for negligence since she has been told that the way they stitched the wound back together was the worst her doctor had ever seen, not to mention the nerve damage. Is this possible since it was a self inflicted wound? I wouldn't want to bring something up that may end up in disappointment and put her back in the state she was in a few months ago.