The Nobody I Married Was Royalty

The wounded man she takes in has no memory of who he is, so she puts him to work in the stables and gives him a name to be called by. He is the missing crown prince. She has sworn off the imperial family. In a life before this one she married into it, and that marriage ended with her dead inside the palace. She is living the same years over again, a noblewoman of a high official's house, and her plan this time is to take a stablehand for a husband and keep away from court. Her younger sister came back to these years as well. The sister goes after the crown prince first, rescues a man who is passing himself off as him, and expects the match to lift her above the rest of the family. The family takes the sister's side and puts the elder daughter out of the house. In the stables the man's memory has begun to come back, and the only standing the elder daughter has to build on is her medicine.