Good guesses, and to answer MaryCas: No, this wasn't on the bar exam though I may raise it in a bar.
The answer is along another track and it has to do with Joan. Not only are Sally and Joan sisters, but they are conjoined twins. Sally can't be imprisoned or executed because Joan is innocent and therefore can't be imprisoned or executed.
OMG, I would have NEVER thought that. Of course, how often would that happen. Still, Sally could kill as many people as she wanted to and get away with it?
That would be a landmark case without a doubt.
TIS
As long as Joan is not guilty of anything, Sally can never be imprisoned while attached to her sister.
Still, Sally could kill as many people as she wanted to and get away with it? 
