The Female Warrior — Doreen Milstead

Many years after the fall of civilization, well, sort of... a young noble woman from Michigonia is sent for to wed the son of a reigning leader of his people. They need heirs. So, she gets married immediately and turns out to be far from the image that her new husband had imagined his wife to be; forthright, willing to produce multiple sons and daughters, and a warrior to boot.