Golden trillium

the long version

The three royal daughters of the Black Trillium brought a welcomed peace to Ruwenda and the World of the Three Moons by defeating the dark sorcerer Orogastus. Now it is time for Kadiya, the Seeker-Warrior, to return the powerful Three-Orbed Sword to its place of origin. But a journey that began in the wild marshlands of her devoted allies, the aboriginal Oddlings, soon leads to the domain of a race of dream catchers created by the inscrutable Vanished Ones—and to the terrible revelation of a coming plague destined to obliterate Kadiya’s world. Unable to contact her sisters and complete the triumvirate, Kadiya must now act alone to prevent the Apocalypse, and follow her destined path into a timeless dimension where the Vanished Ones have taken refuge. There she will confront the most devastating horror her world has ever known. Sequel to "Black Trillium" by Marion Zimmer Bradley, Julian May and Andre Norton