One reason I think Mary is such a well-crafted character is she is so recognizable. I think her hypocondria and always feeling insulted by something or other is strictly a ploy to get attention. Don't you know people like this! Elizabeth gets the most attention from her father for she is so like him. Anne is too genuine and wise to be manipulative and so lets herself be overlooked. And Mary came up with her own method. Manipulative people are always on the lookout for any kind of power over others. They are always protecting no. 1 and so they never mature out of their self-absorption.

I do think though that Anne was a little fond, if not often gently exasperated, with Mary. At least Mary valued her company for whatever reason.