Half-Light, by Denise Vitola.

-- 1992. TSR, Inc., Lake Geneva, WI. Science Fiction.

After Commander Ariann Centuri's betrothed is killed by the Benar, she finds herself stricken by a terminal disease. Her sole chance for survival is to promptly wed the Viceroy of the Galactic Consortium, the only one who can save her life. Their union is stormy from the start, but the warring clans, political intrigue, and outcast nomads of the twilight plane called Half-Light promise to make things more dangerous than Ariann could have ever dreamed. Available through bookstores nationwide or through the TSR Mail-Order Hobby Shop at 1-800-558-5977.