In the first place, the reason why Favored Prince had the guts to say that was because he was sick and from what I understand, it's from this black mist that's spreading out in the plains. So far, there's no known cure so the Emperor was swayed to give in and he decrees that MC Mom has to remarry Evil Dad. Long story short, MC finds a way to negate that decree and kind of browbeats the Emperor by telling him blankly, 'NO, my mom ain't doing that shit' though not in those words. She also points out to the Emperor that she can cure those infected by the black mist and, at first, the Emperor thinks she's bluffing but then she points out that she saved a whole village plagued by the sickness and Evil Dad was there to witness it. Evil Dad gets in trouble for this because he didn't report the whole ordeal which he was supposed to do since he was the one stationed there.