I haven't been able to get the scene of Nettie poisoning you to trigger in any of my patch 6 playthroughs, she always just decides I'm too good a guy to kill now and doesn't even try to poison me. It's a shame because I really liked that scene, it gave Nettie a lot of character.
just pick the options that look like "shut up and cure me ASAP. don't ask questions". she will poison you without hesitation.
