Wind from a Foreign Sky (The Tielmaran Chronicles, Book 1)1997

Gaultry enjoyed the simple, pastoral life of a hedge witch, where her most daunting task was to travel to the nearby village to purchase supplies. But her peaceful life is shattered when it becomes entangled in an ancient prohpesy--a prophecy which names her and her headstrong twin sister, Mervion, as their nation's salvation...or its destruction.