Nokori Ichinichi de Hametsu Flag Zenbu Heshiorimasu: Zamaa RTA Kiroku 24Hr.

Alexandra is the daughter of a duke in the Kingdom of Tarakonensis. One day, she suddenly realized that she was the villainess of an otome game, and it was the day before the climactic event! Alexandra had been bullying the game's heroine with malice, because the heroine had made a move on the crown prince, Alexandra's fiancée. The crown prince seems to have fallen in love with that damn woman, though, and it is obvious that he will denounce Alexandra and break off their engagement tomorrow. But Alexandra won't let herself be condemned that easily! She will show those people who disrespected her what she's really capable of! Now Alexandra has just 24 hours left to make her way out of a desperate situation...

(Source: Alphapolis, translated)