The Wind-Witch — Susan Dexter

Book Two of "The Warhorse of Esdragon"
Faithful wife to a small landholder, Druyan had lived her life in other people's shadows. And if she could sometimes hold the clouds at bay or whistle up a wind, Druyan made sure to keep that talent to herself. Then war came, and Druyan found herself a widow, with no one to help during the harvest but Kellis, the wounded prisoner her husband had locked in the root cellar the day he marched away. But when Druyan freed Kellis from the cellar, she unlocked a Pandora's box, for Kellis had secrets and magic of his own . . .