In the beginning scenes of the play Isabella finds out from Lucio that her brother Claudio is to be put to death for bedding Juliette whom he has not yet married. Lucio tells Isabella that she should speak to Angelo and try to get Claudio off the hook. When Isabella doubts her ability to make any difference in the matter, Lucio tells her, “when maidens sue, men give like Gods, but when they weep and kneel, all their petitions are as freely theirs as they themselves would owe them,” Lucio is basically encouraging Isabella to use her feminine charm in order to help Claudio. Despite being in a convent and knowing that doing such a thing might be seen as wrong, she still immediately agrees to try saving Claudio in that way.
After speaking with Angelo and being propositioned by him (her body for Claudio’s life) she immediately turns it down. When this happens, Isabella says, “I am now going to resolve him. i had rather my brother die by the law than my son should be unlawfully born.” Her wording in this line is very telling. It is completely about herself and has nothing to do with any concerns over her brothers soul. Though she had previously mentioned concerns over his soul, i am convinced that she only says it as a way of convincing Claudio that it is for his own good that she doesn’t sleep with angelo. The way i see it, she is simply trying to look selfless when speaking to claudio there but the line above shows that this is really all about her.