Come Armageddon — Anne Perry

Five hundred years have passed since the events that drove Tathea, the Empress of Shinabar, into exile in the Lost Lands. There she found not only the oblivion she sought, but a chronicle of mystical teachings in a magical Book. She also found her destiny - to spread the teachings in the Book throughout the world, so that humanity would be prepared for the battle against evil the Book foretold. Gifted with the immortality necessary to the task, Tathea has spent centuries dreading that time.
Now it is drawing near. Tathea waits and watches for the Warriors who are to lead the forces of the Light - and for the return of her lost love, who promised to stand beside her during the final confrontation with the Great Enemy. But all of the Warriors do not appear, and her beloved does not arrive. And Tathea is left to stand alone against the Darkness, with the fate of all the world at stake.