Isekai ni Shoukansareta (Nise) Seijo no Watashi wa, Ouji-sama to Kekkon Dekinai to Shinu Unmei no you desu

Office worker Sara braces for what she believes is certain death beneath the wheels of an oncoming truck—only to open her eyes inside a magnificent, unfamiliar castle, having crash-landed directly on top of Prince Ars. Before she can even begin to grasp her bizarre new circumstances, a soldier hails her as "Sara," the saint who saved the kingdom five years earlier, and suddenly the entire court treats her as a living divine being. Then a voice claiming to be a god delivers a shocking ultimatum: win the heart of Prince Ars—a man who yearns for the saint—and marry him, and she will be returned to her own world. Should she fail, she will never see home again. Refusing, Sara realizes with growing dread, might just lead to a bad ending she cannot afford. Her only weapon in this high-stakes gamble is her face, which bears an uncanny resemblance to the saint's. Armed with nothing but borrowed looks and sheer determination, Sara throws herself into a zealous, all-or-nothing campaign to steal the prince's heart.