As others say, the MC is a great char and she's what makes the story interesting, unfortunately, the rest of the characters are not nearly close as polished and at the best of times, the Duke and Prince (the 2 main support chars) seam more high-school kids worried about the prom than nobles that carry the weight of the country in their shoulders. While the MC is mostly smart, thinks ahead, doesn't take things at face value and can at times be decisive, the other chars are moved by pettiness or jealousy, soon forget their position, expose their thoughts and standing at the slightest provocation, they even believe and turn like pancakes at a little acting by the villainess (nobles are groomed to play at words and give little importance to them), and so on. The main weak point in the story imo is the villainess, she's just badly thought out. In the first place, she has no power, no etiquete, no education, no backing (not really, not till later and it's flimsy at best) and she's not even smart, yet all turns around her to ridiculous extremes and all the story thus makes little sense, yeah, there is a rumor going about of her and the Duke, that's all she has going for her and the author makes a mountain out of that ant-hill. Furthermore, Susan gets marriage proposals from many nobles, most likely at least some of high nobility, aka marquess, yet she is set on the Duke which she has no chance of getting and has to get her hands dirty to even try while risking all she has, including her life, why would she be so pent up? she's presented as manipulative and cunning yet is not able to see that marrying another Noble is easier and almost as good as marrying the Duke? Doubtful, she has no reason to be so obsessed unless you consider conceited and whimsical as reasons... they are, certainly, bad reasons of a boring character.
at one point in the plot, the MC has a contract of the villainess blackmailing the church in her hands, along two brigands that tried to kidnap her on the orders of the villainess, whom of course serve as witnesses and finally, the maid that instigated the rumors of the Duke and the villainess having an affair, with all that in hand they decide to do nothing as to dissipate the rumors first... talk about weak justification
Overall, it's entertaining but lacks maturity for the theme it chose imo, also, the art is very good and dialogues are well played for the most part thou a bit base at times. In any case, it's better than some other similar manhwas with the exception of maybe "The duke's daughter accomplishments" and "I belong to house Costielo" (I think those were the names), oh there's also "Empress from another world", the Dukes... and Empress... stories are not exactly the same but have overall similar settings.