If I was your girl in that situation (as far as I can tell, since I never have been in that situation), I would definitely prosecute to the fullest extent of the law, but other than that, I wouldn't know what else to do.
I would also be like her and want to move on with my life and just get over it.
If that was something I experienced, I would not want to relive those memories every day of my life, and I would want to get over such an ordeal as soon as mentally possible.
I can understand your feelings for revenge, but what can you possibly do aside from letting the authorities handle it? Commit a crime yourself by beating the crap out of the guy? don't stoop to his level. Just try to be there for your girl and let her heal. You can't reverse what happened to her, as much as that sucks. The only thing she can do is move on and try to enjoy her life, and be thankful that she still IS alive. that's how I see it anyway.
