The Goodness of Shen Teh

My initial question when beginning Bretch's play, The Good Person of  Szechwan, was: Is Shen Teh actually good?  Obviously, she has better character traits than the rest of the cast.  For instance, she is always putting her owns needs aside in order to help others.  She even  calls off her marriage because it might interfere with her ability to help the neighborhood.  She will not be in love if it comes at the expense of others.  Or so we think.  It is possible that she is only seen as good because everyone else around her is so "bad"?  After all, she is was a prostitute and does live a double life as Shui Ta, who is severe in getting his way and Shen Teh's affairs back in order. Then, at the end of the play, Shui Ta is charged with the disappearance of Shen Teh.  The truth about Shen Teh's double identity is revealed, but only to the gods.  She still refuses to let the towns people know she, too, is flawed.  The god's admit that it may be impossible for anyone to be truly good in the world, so they continue on with the notion that Shen Teh is the only good person left.  They present her to the town as such and disappear.  This last scene indicates that although goodness is impossible, the facade of such a person must be upheld.  The epilogue then asks the audience to decide. What do you think about the goodness of Shen Teh? Is she only good compared to the bad behavior of others? Is her reputation as a good person essential to the play and the society in which she lives?  Have the gods truly created a world in which it is impossible to be good in?