I have to second HSO's comments! As I was reading, the thought crossed my mind that you're reporting about this thing that scared you and nearly, maybe could have been something worse. But you AREN'T reporting about her being assaulted or killed.
That means thing worked out perfectly. I'm not saying that she reacted out of wisdom rather than fear or misplaced generosity. But the fact is, she did whatever needed to be done to find the most positive possible outcome. No death, no blood, no stray projectiles striking others, no trip to the police station, no bio-hazard cleanup, no court appearance, no long-term psychological effects.
She needs to develop the wisest safety practices, and should understand that the time may come that she has to shoot someone or be killed.
But the truth is that the way this ended could not have been improved by her getting the gun, and certainly could only have been worse had she fired that gun.
We often like to talk about having multiple tools in the tool box, and how not every situation needs to have a shooting solution. Your wife had the smarts and capacity to find a non-shooting solution. That's a GOOD thing. She may need to understand the other, less pleasant, tools in the toolbox, but she hasn't FAILED anything. Be proud of her and congratulate her of doing so well.