By The Sword by Mercedes Lackey

A headstrong young noblewoman sees her comfortable life upended by violence and betrayal and is forced to flee; she reinvents herself as a mercenary, rises to prominence as a master swordswoman and commander, and must navigate battlefield dangers, political intrigues, and personal losses while building a loyal company, forging unexpected bonds and love, and confronting larger magical and social forces that shape her destiny.

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