Loyal Portia tries to respect her father’s wishes even though she does not agree with his choices, and even when doing so brings the risk of damage to herself - but she does try to take precautions against this happening. She is not impressed by the standard of would-be suitor - none of them lives up to her high expectations for herself. Faced withthe prospect of ending up with one of them, she uses her womanly wiles and cunning femininity to try to manipulate the situation to suit her desired outcome.
She makes a suggestion to Nerissa: “For fear of the worst, I pray thee set a deep glass of Rhenish wine on the contrary casket, for if the devil be within and that temptation without, I know he will choose it” (1.2.94–97).
She hopes to distract the young suitor from the contents of the box by appealing to his worst nature - the temptation of drink. She thinks she knows him very well, enough to guess that his enjoyment of alcohol will prevail over his curiosity and motivation.
Fortunately, her bluff is not called, and the annoying wannabe bridegroom doesn’t try guessing at the caskets. Portia has pulled off her little ruse, but nowadays adults might want to be more child-friendly and considering of feelings and emotions when planning a young person’s future.
Yes, Portia has been devious and cunning and a bit deceitful herself, but one has to consider the prevailing conditions that are likely to have led a person to such twisted and bizarre lengths. The main one here is fear, and nowadays that is not good in families whether just of disapproval or of real harm. We need to wonder what the outcome would have been if a girl like Portia had had her emotions taken into account-she would not have needed to take a precaution because she would have trusted her family as society would be different.