Reign Check Demon Princess Series, Book 2.

Nikki Donovan was a demon princess. Now she's a demon princess in love. Fresh from finding out she is a demon princess and meeting her father for the first time, Nikki Donovan is looking forward to getting back to her regular high school life. But then Rhys, the handsome teenage king of the faery realm, enrolls at her school as a "foreign exchange student." Her conflicted feelings for Rhys and her boyfriend are getting in the way of her new relat...