The Doomsday Bride's Fortress

She is a substitute bride, pushed out by her family to die. He is the leader of a remnant army at the Frontier, framed as a bandit by the Imperial Court. At their first meeting, he considered her a burden, while she saw his troops' desperate situation. She uses her era-transcending medical skills, tactics, and infrastructure knowledge to turn a dilapidated mountain stronghold into an iron fortress.