A Mere Wife — Zoe Cannon

Two sisters, forced into arranged marriages by their cold and profit-minded father.One runs away to join a mercenary band. The other goes meekly to the arms of her cruel husband.The first sister quickly makes a name for herself. The other learns to cook fancy treats and smile prettily for her husband's business associates... and never to provoke her husband's temper.The first sister is dangerous.The second is deadly.This short story is 12,000 words long. It is also available in Not Your Heroine, a fantasy short story collection.