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.
Have yozu tried insisting on her telling you, what that branch does? That was the trigger before patch 6, I think.
"We are all stories in the end. Just make it a good one."