Enzai Akujo wa Last Boss Ouji no Chouai kara Nogaretai

Orianna, a regular office worker, dies in an accident due to exhaustion and is reincarnated as a villainess pursued by the antagonist in a romance novel.
To evade the tragic fate the malevolent prince has planned for her, she resolves to change her ways and establish herself as a distinguished lady in high society. However, despite her transformation, Orianna is betrayed by her fiancé, Reuben, framed for conspiracy, and condemned. Her unexpected savior from this dire situation turns out to be none other than her nemesis, Prince Dylan.
Even though their alliance in the novel originally led to the worst possible outcome, he is now her only hope. Despite being wary of Dylan's persistent overtures, circumstances force her into a pretend marriage with him.
(Source: POCKET COMICS)