Why does Dolores not die when she gets shot by William?

In the last episode of Westworld season 2 William shoots Dolores many times and she doesn't die. I understand, that hosts don't really die, their bodies just act like they die but their brain is still intact. Dolores probably disabled that function, so she doesn't die anymore.

I also understand that Dolores put Teddies bullet into the gun of William and that's why it backfired. Doesn't William know that Dolores won't get hurt, at least after he shot her once? And couldn't he just have shot her into the head?

But later Bernard "kills" Dolores with only one shot. Is it because the shot was to the head or because he used a special gun? Another thing is that Mave does "die" from a few shots into the belly. Did these special troops use a special weapon which can actually kill hosts or does Mave not have the power to stop hurting? I thought she was almighty over her body too?

Last question: Why do hosts die from head shots (like teddie and Dolores), even if they can stop themselves from dying of body shots? As you can see with Teddies "brain"-core, the pearl does not get damaged from a head-shot so why does Dolores die from a headshot then?