Eternal Vows by Chrissy Peebles

Never marry a stranger...even if he is a drop-dead gorgeous immortal king.

Never pretend to be a princess.

And most importantly...never slip on an ancient wedding ring you know nothing about.

Sarah Larker returns to a cave where her sister disappeared ten years earlier. She walks through a portal and is mistaken for a runaway princess on the run by a dangerous immortal king in medieval times. Her plan is bold as well as daring—become this princess, wed the king, and slip on an ancient wedding ring that will unlock the portal back home. Then find her sister and run as fast as she can out of Dodge. But taking on the identity of Princess Gloria comes along with dangerous consequences; and slipping on the ruby ring comes with an even higher price.

http://www.amazon.com/Eternal-Vows-First-book-ebook/dp/B007HPDFBC/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1334152889&sr=1-1