The what-ifs are very dangerous. In order to defend another person you must be sure they are not the aggressor and did not escalate the issue. Yes, it's probably clear the woman did not attack the man, but you never know, she could have stabbed him when he walked up to her and then he was defending himself... Should I have been in the same situation, I might have asked the woman if I could help her to her car, or walked behind her. If I saw the BG shoot her and then run into a car I would certainly not pursue. If I was in the parking lot, the man shot her and I was unable to call 911 or get to a safe location then there's a different story, but there's just TOO many variables to play what-ifs, especially when it comes to self defense questions. Edit: IANAL