And how do you imagine that, exactly? You think that cop was fine shooting her for driving away in panic, but would patiently wait for her to grab a gun? And what would you like a person in her situation to do with the gun? Shoot him? The fact is, pulling a weapon in front of a US cop is begging to be killed on the spot. A common point of advice is that if you're stopped in the US by police, you should never look like you're reaching for anything, because the worst-case penalty for that is death. It instantly escalates the situation to life-or-death for a group of people that is largely already itching to pull the trigger.
If he didn't have a gun, maybe he would be driven over by the car. Possibly a few more people too. In Europe, where guns are less prevalent, cars are the favorite weapon used by terrorists.
Luckily, he had a gun, so he was able to save himself and who knows how many more people by shooting an attacker.
People in the US get killed at a higher rate than all European countries by vehicles.
The woman who was shot was a democrat without any guns, maybe if she'd had a gun she wouldn't have been shot.