Even if she were completely reformed with no chance of killing more people, the terminal value of her life could still be lower than that of a random person. For example, presumably continuity is valuable (or we wouldn't mind replacing dead people with random newborns), and there's less continuity between evil and good than between good and good; and someone with an evil past will probably experience less happiness during sincere reflection on that past (for some morally relevant value of "sincere") than someone with a good past. It also seems possible that there are components of terminal value that track the game-theoretic reasons you mention: we may terminally value game-theoretically-defined notions of "cooperation" or "justice" on top of their instrumental usefulness.