The Wind-Witch by Susan Dexter

Another one in the same setting series -- the one before The True Knight.  I noticed a few references to fictional history that reminded me of that, but they are both stand-alones.

The prologue being a superfluous link to the first novel, the story begins with Druyan  finding a marvelous black stallion when at a strange garth for a funeral.  She realizes it's Valadan, the legendary half-wind horse, but no one else does.  (She has a little magic herself, being one of those reasons why women were forbidden to whistle; she can produce a storm that way.)

And then we leap forward in time, to when Druyan is holding Splain Garth for her husband while he is in the duke's service, against the raiders -- a band of them had attack the garth, even, and four were captive -- only her husband is accidentally killed by a stray arrow.  And they have no children.  She is thinking of what will happen when she realizes that a widow who holds her lands for a year and a day can lay claim to the lands in her own right.  A serious shortage of hands leads to her thinking of using the captives, only to find that all but one escaped, and that one suffered a head injury.

Kellis, his name is, and he's not one of the raiders' people, and he had other reasons why they had left him behind, that he doesn't go into for her -- he can foresee things, but his predication went awry with the garth.

It winds on, with the importance of getting in the harvest and dealing with the sheep, the continuing ordeal of the raiders pillaging the countryside, the duke's foolish notion of building a fleet to counter them (and manning them with whom?), and Kellis's secrets -- the first one she learns is that he's vulnerable to cold iron.

An interesting tale