Id suggest moving away from attacking the mother, and to actually treating the real sufferer here. Although sueing might bring justice to something that happened years ago, it won't cure or fix her, and it might actually make her worse, creating conflict with her parents.
No one knows the cause of Anorexia. However people do know where it can stem from.
Anorexia is partly influenced by genetics, so even before this person was born, it was most likely she had the brain 'wirings' to encourage such behaviour.
The most you can really do, is support her. Try not giving advise which involves "do this" or "do that" and "you will get better if you do this" - People with anorexia think they are fatter than they really are, they think that being 'that' skinny is attractive. In actual fact men are more likely to choose women far larger than the underweight stature of someone with anorexia.
Support and helpful advise will do wonders if you do it right. You can't change her body image for her, only she can do that. What you can do is support her, and reinforce positive beliefs that she expresses.
Try and stay away from being too much of a 'baby talker'. No one likes being over sympathised with, because it just seems far too fake, and belittles them as if they don't KNOW they are skinny.
If anyone wants immediate advice don\'t hestitate to contact to me on AIM (AOL instant messenger) - aim: vodkasmodka
Eccentric! Not egocentric!