In Shakespeare's Merchant of Venice, did Portia do the right thing by giving Bassanio a hint so that he may choose the right casket?

The real question actually is, does Portia give Bassanio a hint? When she meets him, Portia unequivocally states:

I could teach youHow to choose right, but I am then forsworn;So will I never be:

Her father's will expressly stated, as she told Nerissa earlier:

... I mayneither choose whom I would nor refuse whom Idislike; so is the will of a living daughter curbedby the will of a dead...

The real question actually is, does Portia give Bassanio a hint? When she meets him, Portia unequivocally states:

I could teach you
How to choose right, but I am then forsworn;
So will I never be:

Her father's will expressly stated, as she told Nerissa earlier:

... I may
neither choose whom I would nor refuse whom I
dislike; so is the will of a living daughter curbed
by the will of a dead father.

Obviously, Portia had to take vow a to never break any of its conditions. She therefore tells Bassanio that she will never break a vow and be 'forsworn,' which means she would then be disowned. Her father's estate will therefore be denied from her. Portia is obviously a decent and respectful person and sets a very high moral standard. To emphasize the depth of her conviction, she states further:

 ... you'll make me wish a sin,
That I had been forsworn

She is saying that should Bassanio choose the wrong casket and 'miss' her she would have wished a sin, which would be to help Bassanio and she would then have been disowned. Except for her moral conviction in this instance, there is also the possibility that she will lose everything.

There is a suggestion though, that the introductory words to the song sung by Portia's minstrels are supposed to give Bassanio a clue:

Tell me where is fancy bred,
Or in the heart, or in the head?

The words, 'bred' and 'head' obviously rhyme with 'lead.' There is no indication from Bassanio though, that he had taken heed of this purported 'clue.' His entire monologue focuses on the contrast between appearance and reality. He speaks about how deceptive things are and that which seems genuine is most often fake or that we find value in something which is actually worthless. It is for this reason that he chooses neither the gold or the silver casket, for they may represent something which they are not whereas lead is just that - lead. It is unpretentious and real.

Furthermore, there is no evidence in the text that Portia had given her minstrels any instructions to assist Bassanio. It might just be coincidental that the song commences with these rhyming words. Shakespeare might have just created the rhyme to add some drama and create a conundrum. If Portia should have given Bassanio a hint, she would have broken a vow and the terms of her father's will. She would have been disowned.