The Key in the Loch by Blanche Dabney

The key to understanding the past is to live through it…
History student Rachel Fisher has dreamed of the past all her life. When a mysterious box sends her back through time to twelfth century Scotland she thinks her dreams have come true, especially when she falls straight into the arms of a burly Highland Laird who vows to protect her from the evil that’s chasing her.
Grizzled warrior Cam MacGregor knows one thing. He must not fall for the beguiling lass with the flaming red hair. Already whispers are spreading among the clan. He has taken her in because she’s bewitched him. The omens are coming true. The Sassanach does not belong. She must be sacrificed.
In a world that wants her dead, Rachel’s only hope lies with the brawny Highlander. As their mutual desire grows into an all-consuming need, Rachel is forced into an impossible choice. Save herself and run from the man she’s come to love or sacrifice her own life to save his clan from oblivion?