Portia is an intelligent woman trapped in a man's world.
Yes, Portia is smart, observant, clever and strong-willed. She is from a noble family, has married into a noble family and is well educated in the spheres of the domestic and the political.
Portia is an unusual Shakespeare female character in that she does not perfectly fit the mould of the typical tragic female who is often characterized as being overly-romantic, unable to form her own opinions, and hysterical due to her inability to control her emotions.
Portia is different because she is the polar opposite of a typical tragic female character. However, she must still conform to the patriarchal world in which she finds herself which is why she can never truly be Brutus' equal. In the end, when Portia kills herself by swallowing hot coals, she is totally alone, having been abandoned by her father, Caesar and her husband. Without a male figure to attach herself to in order to justify her existence in the play, Portia is no longer useful and so subscribes to the hysterical female character trait and kills herself in a gory final act.
Portia is a strong-willed, stubborn, persistent and shrewd woman--all uncommon characteristics in the stereotypical woman of Shakespeare's time. Portia confronts her husband in their orchard, in the middle of the night, in the rain. She will not accept his excuse that he's sick--if he were, he wouldn't be out in the rain in the middle of the night. She's noticed a change in his behavior--he's moody, sullen, and silent--and wants to know the reason for it. When he says he can't tell her, she uses various persuasion tactics to get him to tell her. She cites her lineage--her father and husband are strong, so she is strong enough to know his secret. He chose her as a partner and they took marriage vows, so that should be enough reason to tell her his secret. She even goes so far as to guilt him, saying that if he's not going to talk to her, and just use her to eat with and sleep with, she may as well be his prostitute rather than his wife. Her last effort to prove her strength is to prove her physical strength--she gives herself (or has given herself) a wound in the thigh with a knife. She asks if "can I not bear this and not my husband's secrets?"