with her backtalking like that- its more petty but with shenanigans and the pair of siblings. FMC will have the "right" in helping the emperor give a lenient punishment for the princess.
I feel he's be hasty in this marriage- sure it's a cop out to a quicker solution, in fact I can't imagine him proposing in a less urgent occasion. I just think that he taking advantage of the situation, there are times where this story seems cliche but for "pace convenience" it's OK