Patricia A. McKillip 
Cygnet and the Firebird [EPUB ebook] 

The firebird came at night – a magnificent creature whose magical cry seemed to transform objects at random. Gifted with powers of her own, Meguet tried to reach out to the bird. But at moonrise, the firebird became human, a prince cursed by dark magic. Meguet bowed to help him. But then the mystery carried her away, on alien winds, to a land far from her home…At the edge of the world, the Luxor Desert awaits – a barren land where a sorcerer’s war rages. Where invisible dragons cast shadows over ruined castles. And where Meguet’s own fate depends upon a secret locked away in a tower for centuries…