]Mary might not have had what it takes to be the brilliant, accomplished woman she dreamed, but why would she not be able to pick up on her father's disdain for her mother just as Lizzie and Jane had?

I've always seen Mary as someone who decided early on in life that she would never be pretty and never be popular, so she decides to be smart to distinguish herself. As with many people who lean heavily on "book learning," though, she lacks common sense and people skills. Whether consciously or unconsciously, she chooses to be on the outside looking in to social situations - at the Meryton assembly in P&P2 A.D. shows her sitting on the sidelines looking prim, not dancing or conversing. So I would guess that she has virtually no powers of discerning what her father's or anyone else's actual feelings are. She has no direct experience in the feelings behind manners, she only knows the forms. In my imagination, she thinks of her father as sometimes ill-mannered, sometimes witty, but I doubt she ever puts much thought at all into why he speaks ill to her mother or what he feels about her.