This type of injury is why I don’t think it should be held against someone for being the one to “introduce a weapon” while defending themselves.
In such a situation, it seems you must prove you feared for your life, instead of simply recognizing that it was in danger.
Most people are not body builders, nor trained in hand to hand combat like police. I can see a cop being expected to take a slap or two before drawing a gun, but not the general public.
Look at the video from post 17. You will see that this was such a completely unprovoked attack that no sane person would have had time to have drawn on the attacker. She was truly an innocent bystander.