The Emperor's Lady-in-Waiting Is Wanted as a Bride (Manga) Volume 2 by Kanata Satsuki

Lyse was once a knight who gave her life to protect the young emperor-to-be and his closest friend, and now she’s been reborn as the daughter of a humble baron in one of the empire’s vassal states.

She means to keep her distance from all things imperial and keep her past life a secret, but when she crosses paths with the emperor again...she finds herself engaged to one of his knights and privy to a secret of royal proportions!