The Sahra Chronicles: Fire of the Gods:

Sange, sister of Arak clan chieftain Javrik, has followed her husband, Arman, to his native land. But her people half a world away are occupied by forces of the mighty Empirate of Omana, and now she is in Alcinia, an ally of Omana. The Emperator's sisters hold powerful positions there and, belatedly, she realizes that she and her infant son are hostages.