Might I ask what certainty you are looking for to justify self-defense? What would be a likely scenario?
As I see it, the man was walking right at her with a gun pointed in her direction. How is she to know whether he is just being a "tough guy" or looking to harm her physically, either through harsh beatings, rape or murder? Even if he is someone only trying to act tough, I would think with all the gun topics on this forum, people are fully aware how easily a gun can be fired by accident when people are acting irresponsibly.
Waiting for that certainty you mention likely means it is already too late, as they have already caused harm in some manner for you to realize they aren't nice people. They certainly won't be discussing their actions beforehand so you can be better prepared
To be honest, I'm not planning to post more in this thread (as I'm just repeating myself), but appreciate the way you framed the question.
Unfortunately, I cannot comment much on this particular case, because the video starts with both her and the assailant already pointing to each other. I do not know what happened before that. She obviously noticed something ahead, otherwise she wouldn't (one would hope) have a gun at hand. So, that lapse of time missing is kind of important.
Of course, if all happened in a second
(and it might have, since the space between her "room" and the entrance seems to be just a few meters), and she suddenly found herself in front of a person aiming at her, the reaction would not only be justified, it would be an instinctive one.
But again, I'm not questioning her actions. She did what she did, and that's the end of it.
I'm however, not ok with the idea that people (already armed), being called "
brave" for shooting first. There is simply, nothing brave on that. And -depending on the circumstances-, a reckless call to make.