People are also assuming that she wasn't familiar with weapons before hand.
I was shooting rifles and shotguns before I was ten years old. It's not that uncommon for people from the States to be well versed in the subject without having law enforcement or military training.
It isn't really like she moved militarily, she just pointed in the right direction and got one in OPS, and then went full mom mode in the hive. I honestly have less problem with that aspect than most people do. Because what she did isn't hard. Of all the things you could face militarily an 8' tall enemy that rushes right at you is probably the one you want after you. It's a big target. What it does if it catches you is horrific yes, but until it gets there that advantage is yours.
Moving tactically is harder than basic marksmanship.