Her mistake was saying "maybe it wasn't the best decision to make".
If you're going to pull the trigger, stick to your guns. They were violently assaulting her and she was in fear of her life and the life of her daughter. If David can take down Goliath with a stone, 3 grown "kids" can kill or seriously harm an adult with rocks as well. I'd have shot too, but it wouldn't have been "shooting in their direction", there'd be bodies on the pavement.
I have a nice scar from 76 stitches that it took to patch the hole in my cheek from where a ~15 year old kid threw a stick at me, and had a nice concussion to boot. According to the surgeon, I got seriously lucky, as it missed the most major nerve center, salivary gland, and artery in the left side of my face by mere millimeters due to the way the blunt object cause the flesh to tear. Also exceedingly lucky that one of the best and most respected reconstructive surgeons in the state on on-duty at the hospital that night.
No, if you throw things at me, you're going to be looking at my firearm, because the only thing I'm throwing back is lead. Personally, I'd at least *try*, if the situation allows, to warn off my attackers before pulling the trigger (hence I've pointed my gun at someone in self-defense on three occasions, but never pulled the trigger because they obeyed my commands), but if you keep doing whatever it was you were doing to make me draw on you, you're going to find out quickly that "command" means "non-optional - consequences
will apply".
Frankly, I've never had much in the way of empathy with or pity for people who complain about getting shot for throwing rocks at people with guns, whether they're teenagers, or protesters: if you mean to hurt someone and/or make a statement, then either accept the consequences, or go all the way. You don't get to say "well, a rock isn't going to kill anyone! Not like bullets!"
Then again, I don't believe in fist-fights either, especially not as a means of conflict resolution, and never have - and never will - accept the "it's just a simple fist fight, just duke it out and settle it." No. I will not fight you unless given no other choice. I'm not risking my health, well-being and ability to care for my family just so you can try and prove something. Might doesn't make right, nor does you being bigger, stronger, and more violent than I am.
Still, hard to judge whether this was a "good shoot" without more information and all sides of the story, but it doesn't appear she gave any warning... not that I'm sure one was required if she was, in fact, under a hail of flying rocks... that's a forcible felony, right there, and nothing in the law requires us to tell someone who is committing said forcible felony we're about to shoot them. Fact of the matter is, they were engaged in assault with a (potentially) deadly weapon, and it's no different than if they'd been shooting at her, or throwing any other dangerous object.