I'll be honest, it's been a while since I watched this show. My grandmother and I watched it together when it first came out and she now owns the entire series on DVD, but I haven't sat and rewatched it on my own since before the first movie came out (which I still haven't seen). In short, my memory is fuzzy.

When Cora, Anna, and Mary were leaving Panuk's room, Cora tells Mary she can never forgive her for what happened that night. The way I read the situation was that she refused to forgive her for asking her to carry a dead man to his room to avoid scandal, though I guess she could have also been referring to Mary being intimate with Pamuk before marriage. I've just finished the episode and I wonder, does Cora ever forgive her daughter at some point? Beyond Matthew finding out later on (and that newspaper guy blackmailing Mary later, too, iirc), is it ever brought up again?