Barkson's Journey - Kristine Kathryn Rusch

When Augusta (Gussie) Kirilli discovers that someone wants to destroy her entire family, she has to warn them. But they're scattered all over the Qavnerian Protectorate. So she hires the one person who can reach them quickly-Lucinda Barkson. Lucinda Barkson, tough and dedicated, with a mysterious past. Lucinda Barkson who sets out immediately, armed with fourteen letters, a partially accurate map, and a dozen different weapons. Lucinda Barkson, who soon realizes she faces warriors from the greatest military in the world-the Fey.