A valid concern. If she's going to be armed and consider responding to a threat, she needs to have a means of NOT violating rule #4. That would be, at the very least, a light that would illuminate her target...either hand held (not ideal with a shotgun), weapon mounted (possible but expensive) or positioned in the bedroom (like a lamp that would illuminate the doorway clearly).
You NEVER shoot unless you know what you're target is. Period.
You would also need to go through a few scenarios with her if she's going to be a participant in any 'home defense plan' and make sure that she is confident and capable with what she is using and what she is doing. This doesn't happen overnight, but skimping in this area can be deadly. Don't think that just because you have the toys that you can play the game. Practice practice practice!
Mike