I need to get out my copy of Measure for Measure to study this deeper, but allow me to make a few quick points. First, Measure for Measure is one of the problem comedies written by Shakespeare where there The Duke and Isabella are wed. Under this justice/injustice binary the reward for not committing a crime is a marriage.
It seems clear that underneath the text of the play exists a world of male dominance. The women in this play are prostitutes, nuns, or jilted lovers that have no control over their lives. Rather they are controlled by men who pay them money, a male-dominated religion, and men who continue to control the heartstrings of their former lovers. Isabella shows a sense of independence in her refusal to Angelo's advances, "Better it were a brother died at once/Than a sister, by redeeming him,/Should die for ever." (II, 4, 107-109). Unfortunately it was not independent at all. Isabella seeks her brother's advice and does not act until there is advice from The Duke and Friar.
Isabella is dominated by The Duke throughout the play leaving it clear that she'll accept his marriage proposal. The Duke was ultimately the one who devised what would be the bed trick as he suggests, "We shall advise this wronged maid to stead up your/appointment, go in your place." (III, 1, 241-242). Isabella submits to any of the Dukes ideas.
The Duke did lie about his appearance but he did it for reasons good purposes and justice rather than something that would constitute an injustice.
Again, I need to reread the play and think about this more. It's been about 3 years since I read it, so I could be off on a few of my ideas. Of course, one of my favorite lines in Measure for Measure occurs in the third act:
Sweet sister, let me live.
What sin you do to save a brother's life,
Nature dispenses with the deed so far
That it becomes a virtue.
(III, 1, 134-137).
Indeed Claudio, indeed, sin is a virtue.
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