Although that's a hilarious gif, I don't think it's all that bad. And I agree with you, Joe. The latest edit is safer, but not quite as dynamic and exciting. You may be right that it would be better to move her head back, so you could still keep her shoulders pulled back as in the original. But pulling your shoulders and head back implies that you've trying to avoid someone hitting your head or chest, like Neo dodging a bullet in the matrix.
If you're trying to avoid a low blow towards your stomach or pelvis, it makes more sense to lunge your arms forward as you shoot your hips back.
(Couldn't really find a good example of this. I have no idea what I should google

)
The direction you move your arms would depend on whether you're trying to move your head back or hips back, as you use your arms to get momentum.
I'm going to be quiet now. Like I said initially, I'm useless when it comes to anatomy, so I shouldn't giving advice. All I can say is whether I think something looks strange.