Friend: Esther not only married someone outside her faith & people, but likely had sex with him before marriage (Esther 2:12ff).
Me: I think the situation made the whole thing forced on Esther's part. If she refused to go along at any point she would have been executed, so she was justified in submitting to immorality. Death/suicide is not the only morally justifiable way forward in such cases. One theme of the book is that God can bring good out of messy situations where you are forced to do wrong (POWs working for the enemy, etc).
Friend: "justified" is a word that would indicate Esther's premarital sex & marriage with a non-believer to be not sinful. This seems to suggest sin is relative to the situation instead of the act itself. Moreover, is it not better to die than sin?
Me: So every prisoner in the Nazi camps was morally required to commit suicide? To continue to live would be sinful? No way. The fault lies with the oppressor, not the oppressed, for the sin enforced. And, analogously, as prisoners making ammo for the enemy would sabotage whenever possible, so Esther sabotaged Haman, when God providentially put her in such a position.