Her Highland Prophecy by Eloise Madigan

Three-hundred years into the past, she found him…

When a gypsy hands her a medalion at a fair, Diana Huntigton thinks it nothing but a trinket. Until the moment it transports her back in time and straight into the arms of a very bewildered, very handsome Highlander.
With his clan on the brink of destruction, Gordain Boyd has to find the necessary funds to save his castle. When a strange Englishwoman comes to him with an earth-shattering revelation, he strikes up a deal in order to keep her secret. There is only one problem: what he really wants to keep is her.
Diana’s imminent return to the future is not the only thorn in their side. Amongst escalating unrest caused by the passing of Gordain’s father, a rumor arises that demands her death at the stake. With the clock ticking, Diana is asked to make the ultimate choice: return to her original time or watch Gordain perish.