Marycat and Constance are joined at the hip but then kind of like you only view them through Marycat's lens means that the community can never actually know them or really relate to them which might create a two-way street. The movie plays this up a little bit more it's sort of implied that their dad was not like a great dude okay sure but they just don't talk about it that much I think you can infer based on the way that Marycat responds to Charles that there is some kind of real or perceived injustice that she suffered at the hands of her family.