Demilka-sama wa Goritsuyo Akuyaku Reijou: Mental Saikyou Ojousama wa Ouji kara no Konyaku Haki wo Buttsubushimasu!

Lady Demilka of the Grandcheddo Ducal House is a flawless beauty, intelligent, and possesses an unshakably strong mind—truly the ultimate noble lady. Since childhood, she received elite education as a candidate for crown princess and never doubted she would marry into the royal family. But when the timid prince unexpectedly rejects her, she should be heartbroken... Except she's not. With perfect composure, she boldly moves to crush the broken engagement!

(Source: Coamix, translated)