All good points so far, so let me throw a monkey wrench into the mix:
Civil law has a concept called the "eggshell skull"
rule, which basically says an attacker takes the victim as he finds him -- that when someone commits a negligent act that leads to another person getting injured, then that person is culpable for the entire extent of the injury even if the victim had some pre existing condition that turned what should have been a minor problem into a major one.
In criminal law, a similar doctrine applies in self defense. If you have (for example) a bleeding disorder, the attacker doesn't have to know he is putting you in legitimate & reasonable fear for your life if he threatens to punch you. You
simply have to know it and be able to articulate your reasonable belief that the person about to punch you in the head was actually about to use deadly force against you whether he fully realized it or not.
Seems to me that the eggshell skull doctrine comes into play on this one. The clerk didn't know & couldn't have known that the woman had put herself into a physically precarious condition, but IF
it's found that he used too much force, he's on the hook for the entire consequences.