Unchained (Elf Slave #3) by Sarah Hawke

The continuing adventures of Elara, an elven sex slave blessed with rare magical abilities.

Elara travels to the Imperial province of Korvale in a last, desperate attempt to secure the loyalty of Aemond Darkstone, the Vale's legendarily depraved ruler. But shortly after her arrival, Elara uncovers a secret so profound it could destroy the Empire from within - and she quickly realizes that the perverse appetites and vices of the Duke's family are now the least of her worries...