It's a josei where the main character was like a knight or something then she is betrayed and killed by her companion and she is reincarnated as a noble lady in the enemy nation and she wants to take revenge on the person who killed her.
1 Answer
You may be thinking of From a Knight to a Lady.
From Baka-Updates:
Estelle meets her untimely death as a valiant knight of the Kingdom of Ersha. But death is not the end for Estelle -- three years after her demise, she finds herself reincarnated (transmigration) in the body of Lucifela Aydin, the spoiled and cold-hearted daughter of a count in the Empire of Jansgar. To her dismay, she finds that her country fell to Jansgar years ago, and that she is now betrothed to Zedekiah Heint, the son of a duke and her adversary in her previous life. Can Estelle discover the truth behind her death while attempting to navigate her new life as Lucifela?
The main character, Estelle Schubert, was a female knight who was stabbed and killed by someone she believed to be an ally. She then wakes up three years later in the body of Lucifela Aydin, a noblewoman from a rival kingdom which had conquered Estelle's kingdom in the intervening period.