We were always trained to not squint through one eye. We were also encouraged to use both hands, when possible, because it creates a more stable shooting platform.
Oh, I see what you're talking about now. Nevermind.
Was I the only one who thought she was winking at me?
Examining the picture closely, you'll see that while she does have her off eye closed, she is not squinting. The two handed grip is mostly an American thing, at least in police circles. It does provide a more stable hold, but sometimes, often in fact, you need your other hand for something else, say grabbing your handcuffs, or holding onto the dog's leash, and so you shouldn't be limited to the two hand grip.