The Question and Answer section for Julius Caesar is a great resource to ask questions, find answers, and discuss the novel.
Shakespeare has a tendency to portray strong women, who interject themselves into the lives of their husbands or lovers. These women add a dimension that is often lacking in tragedies..... a realism.
Portia's actions give her a presence..... she isn't a mere woman, she is Brutus' wife. Because of the way that Shakespeare develops her character, she isn't just Brutus' wife, she becomes as extension of the man.
Portia appeals to their vows, her trustworthiness as a wife. her nobility, and her status as Cato's daughter.