It seems to me that your sister hasn't yet even faced the decision of whether or not she is willing to use lethal force. That may take some time. I know of people who swore that they would NEVER use it and after some serious contemplation, have changed their minds. The question is not an easy one. She needs to look into it a lot. I will reccomend a book by Massad Ayoob titled Stressfire. While it deals primarily with (obviously) the use of lethal force via a firearm, it delves into the physical and psycological aspects of it. Another good book IMO is his book In The Gravest Extreme. It too deals primarily with Firearms, however it too speaks of when you may need to use lethal force. They also talk about what to expect afterwards...legally and emotionally. Whenever I taught firearms classes I'd strongly reccomend reading them. Although they are both relatively small in size....They read very well and easily but provoke a lot of thought.