The Shadow — Marion Zimmer Bradley

After spending her youth in the Terran Empire, Margaret Alton returns to Darkover, the planet of her birth. There she discovers she has the Alton Gift--forced rapport and compulsion--one of the strongest and most dangerous of the inherited Laran gifts of the telepathic Comyn--the ruling families of Darkover. And even as she struggles to control her newfound powers, Margaret finds herself falling in love with the Regent to the royal Elhalyn Domain, a man she has been forbidden to marry, for their alliance would irrevocably alter the power balance of their planet!