Lightning's Daughter — Mary H. Herbert

Gabria's epic magical duel with Lord Medb has seemingly done little to change the opinion of sorcery amongst the clans who inhabit the Dark Horse Plains. But when the problems of the faraway city of Pra Desh threaten to spill over onto the plains, the clans ask Gabria to intervene.

With the help of the intelligent, magical Hunnuli horses, Gabria and her companions set out on a difficult journey to seek a priceless tome of magic. If she can overcome the threat to Pra Desh and the clans, Gabria may be able to win a place for magic in her world--if not, the Dark Horse Plains will be destroyed.