Mike, I am glad your friend noticed the danger signs and reacted appropriately in a timely manner. There is an old saying, "friends do not let friends carry mouse guns" sure they are cut, but anything less than 9mm/38 special is a mouse gun.
I was working as an inner city cop when I learned that staring down the barrel of a 357 magnum does not impress some people. What I did learn is that by lowering my aim to the groin helped some people through the decision making process faster and with a much safer outcome. Not that I was going to shoot there, but they did not know that.
As with any other form of self defense you must be very alert to your surroundings. If the first clue you are under attack is the BG charging you then you failed to pick up on numerous danger cues. The woman that Mike mentioned picked up on the danger cues and listened to them and in all likelihood it saved herself a lot of grief and pain.
If suddenly thrust into a violent encounter most people will react exactly as they have trained and/or practiced. In a purely reactive fight, more than likely you will not be aiming, you will be looking at the threat and shooting at the threat, that is why in real gunfights so many cops and robbers are shot in the hands/arms and guns get shot.
My rifle and pistol are tools, I am the weapon.