Tathea Series by Anne Perry

She was an empress-until she lost everything. Now known simply as Tathea, she will wander the Lost Lands and become empowered by the teachings in a book-a book will that guide her onto a path even greater than the one she walked as a ruler.

Tathea, the Empress of Sihinabar, has wandered the Lost Lands for five hundred years, spreading the teachings of a mystical Book to prepare mankind for the inevitable battle with the Great Enemy. Now that battle has come, and Tathea must stand alone.