The relationship between Portia and her father can be described as traditional, but loving. Despite her great intelligence and fiercely independent streak, Portia defers to her late father's wishes as was expected of a dutiful daughter at that time. But in complying with her father's instructions—as can be seen in the casket challenge, for instance—Portia isn't just blindly following the dictates of convention; she's acting out of genuine love and respect. She realizes that her father, in devising the challenge, had her best interests at heart. (Though it's telling that the independent-minded Portia needs to be convinced of this by Nerissa). He wanted Portia to marry someone who'd genuinely love her for herself and not for her money. The casket challenge is a way of weeding out all the many fools and gold-diggers who Portia's father knew would beat a path to her door, and leave the field clear for the man of her dreams.