It has some relation to "monkey see, monkey do" in that learning takes place through the observation of others in order gain an understanding of the social world, of concepts, and to better fit in during novel situations. Observational learning occurs when a lack of understanding is replaced with new information gained from the environment. It covers how to behave in new situations, what objects mean, how to avoid pain and embarrassment, so many things just gained from observing others. You see on TV a person locked out of their house and try to pick the lock with a paperclip. At some point, if this happens to you, you'll probably fish for a paperclip in your purse too because at a prior point you assimilated "lock pick" into your concept of "paper clip". Watching MacGyver taught us all a dozen new tricks with duct tape.
Now, those explanations are simplistic. Observational learning is more than just mimicry. It develops and expands pre-existing concepts (referring back to paper clip). And this is where I get back to guns, as a concept.
There are probably people on here who've never seen a gun in person, let alone handle and fire one. But they understand what a gun is, what it can do, and they have a basic understanding of how to make it work - pull the trigger. Just alone through watching television and video games, an object's meaning grows and becomes more complex. Through each observation, we expand our concept of guns and learn how it kills, how people can suffer from it, or how it saves lives. This occurs without ever being explicitly trained or told what to think.
For the person who's never handled a gun but was put in a life/death situation, using the gun would be mimicry "monkey see/monkey do". They may not know how to remove the safety, or shoot well, or what to do if a cartridge jams,
but through seeing guns in pretend action, they have a preconceived concept that a gun will fire a bullet and harm or kill a target if the trigger is pulled. A gun can stop a bad person.
Getting back to the girl saving her mother's life, she most likely had a preconceived concept of
what guns do as I just mentioned. Her very exposure to popular culture already gave her an understanding that pointing the gun and pulling the trigger at this man could stop him from hurting mom.
Watch a small child play with a new toy gun for the first time. Chances are he'll go "bang, bang!" if his parents ever let him watch cartoons or adult TV. Although now they'll be mimicing laser sounds! "Bzew! Bzew!"
That is enough brain-stuff for one night. lol