Portia's prosecution leads to entrapment. She doesn't have any mercy for Shylock. She only tells Shylock to show mercy on Antonio. (4.1.177) 'Then must the Jew be merciful.' Shylock then askes her why he should. She answers with a speech about mercy's attributes saying 'It is an attribute to God himself,/And earthly power doth then show likest God's/When mercy seasons justice.' and continues to talk about the Lord's Prayer, possibly trying to show that Christianity is better than the Jew. Shylock says 'I crave the law,'. Portia and Bassanio offer Shylock 'thrice thy money offered thee.' That is when Portia executes the entrapment. I think she never believed that Shylock was going to take the money offered and her opening was for show.

Portia uses Venitian law to pretend she's on Shylock's side. 'Why, this bond is forfeit,/And lawfully by this the Jew may claim/A pound of flesh, to be by him cut off' She gets him excited that he is going to be able to get his bond of flesh. Shylock compliments Portia over an over 'O noble judge, O excellent you man!' 'O wise and upright judge!' Portia then starts to mess with Shylock and his written bond bringing out uncertainity with both when she asks him if he has brought a surgeon. Then slams him with the law of shedding Christian blood. (4.1 lines 300 -307) Telling him he HAS to cut the flesh because he refused to take the money. 'And you must cut this flesh from off hsi breast./The law allows it, and the court awards it.' and continues to tell him to get ready to cut off Antonio's flesh. When Shylock back peddles and no longer wants the pound of flesh, just the money, Portia finishes him off. 4.1 lines 342-358 She talks about Shylock, as an alien, wanting to take Antonio's life, is punishable.

Portia indeed entrapped Shylock and it was well done. She wouldn't have gone in as Balthasar if she didn't know what she was doing. In the entrapment, she saved Antonio and beat down Shylock. Besides I'm not sure if she is capable of mercy... She requests that Bassanio give him her ring (disguised as Balthasar of course). She also mocked all suitors that came knocking on her door. Regardless, I think she makes a wonderful heroine.