I have carried a sidearm ever since my military days and have needed to fire it in self-defense several times. But I have a very mottled past, not very normal.
What I do know is that legal liability issues creep into even law-knowledgeable military operatives and civilian police officers' actions and decisions, let alone a 6 year old little girl's. There are many gray-area ambiguities that appear in society today.
Someone threatening you has a gun. Can you shoot first? A knife? A hammer? A fist? When can you use lethal force?
(By the way, in a knife vs gun scenario, if the person in possession of the gun also has a taser, the gun may not legally be fired first.)
Here in Toronto several years ago, a crazy kid wielding a knife on an empty downtown street car was confronted by police demanding that he drop his knife. He refused and was shot at and struck three times by one officer when the boy took steps forward... which was legal for the police officer to do. After the crazy boy fell, the remaining six shots fired by the same officer was construed as murder, etc., and the police officer was convicted.
A man caught a burglar climbing in the man's bedroom window and shot the burglar who was unarmed and, dying, fell back out the window. The man defending his home was convicted of murder because the body did not fall inside the house.
There are many gray-area ambiguities that appear in society today. It's why I don't carry a sidearm today. Plus, I'm Canadian and have little need for one; I haven't even been killed once yet.