The Spellsong War

The Spellsong War, the second book in New York Times bestselling author L. E. Modesitt, Jr.'s epic fantasy series the Spellsong Cycle about a singer and music instructor at Iowa State University who gets far more than she expected when she is magically transported to the world of Erde.
Anna Marshal is regent of the kingdom of Defalk only a few months after a sorcerer pulled her from her boring life as a music instructor. Her power and abilities saved Defalk from invasion, and now she must defend it against the greedy rulers of neighboring kingdoms who see an opportunity.