I think i have covered most of this Jane.If she pushed the rifle at the last minute,it would be the barrel.To change the angle of the shot she would have to reach out and move the stock end.However,changing the angle of the rifle would not have prevented her being shot,she had to push the barrel away from her throat to achieve this,and obviously she didnt.So i dont think it is logical to think she altered the angle of the shot in any way.Thats how i see it anyway.
Had the first shot been immediately fatal, she'd no longer have been capable -or worried- about placing the rifle for a second shot, would she? If it hadn't been immediately fatal, how, with damaged vertebra, would she have managed to lift her arms to reposition it, then stretch one arm out to push the trigger again, whilst keeping the rifle aligned in a better for killing position? Whilst you appear to be applying some sort of logic, here, I doubt Sheila would have been capable.