DD would probably fall over trying to catch like this. she generally tries to have throwing hand meet the glove at about armpit level, as she is rising to throw. also, throwing hand behind glove might protect hand, but then rest of arm, especially elbow, are very exposed. with hand on ankle, it gives her arm a little protection from her leg as well.Behind the back is safest. But only if you intend to catch and block 100% of the balls one handed.
Even with the hand tucked into a shoe or shin guard strap, it's going to be exposed on nearly every swing, b/c human instinct is to bring the hands together. That hand is going to fly up and be hanging in mid-air, as much as she tries to keep it tucked away.
Break the tendency early, and learn to keep the hand behind the glove, then pull the hand back to the chest so that it's always in the gloves "shadow".
In one of the previous iterations of this topic, another poster highlighted a key point: yes - if you have to reach far to the left or right, your hand will be exposed. However, how many hitters will be swinging at pitches where the catcher has to reach that far? And if the catcher has to reach that far, how many batters will actually make contact? And of those contacts, how many of those will be a foul ball directly back to the catcher? We're probably in the .001% by this point.