In Chapters 1-3 Esther comes off pretty badly, here there seem to be some evidences of grace as she seeks to live in line with God's promises. She illustrates well the dangers of making examples of sinful human beings in the Biblical narratives. She has flaunted her position and married a foreign king... but now she will seek to use this position for good.
How do we know the difference between the good and the bad? Our discernment surely comes from what God speaks to his people. Here it seems that Mordecai has been acting in line with God's promises - absolutely sure that his people will be preserved by God, and that they cannot bow to the Amalekites. Risky strategies to bring these things together appear to shape his actions.