I don't have a step-by-step guide for this, but for lack of any other information available right now, it's worth mentioning that you CAN earn this in single-player theatrical cut mode. Barely. Basically, whenever you are playing as Angela, pick whichever dialogue option seems the least bitchy. I was simultaneously trying for the John & Angela max relationship achievement (which I came just short of earning), so I also made decisions like going with John into the foggy bridge at the beginning, and choosing to stick with him and Andrew rather than splitting off with Daniel and Taylor. I'm not sure whether or not these influence her Understanding trait.
There is an optional dialogue that I do think it's important to get. When you're walking down the road during the early chapter Confrontation (before you reach the foggy bridge), Andrew comments "we might get a better view from up there" and walks off to the little overlook. Make sure you follow him and have the optional conversation with him, as this presents an extra opportunity for Angela to be nice.
Otherwise, pass QTEs so that you keep Angela alive until everyone gets to the burned house at the end. It wasn't until I said "hurry!" to John (over "I'm not waiting for you") when they're both fighting their demons outside that this achievement finally popped for me...literally the last dialogue option you have as Angela.