The Highland Rogues: Warrior Bride by Lois Greiman

Lachlan MacGown has been long suspicious of the mysterious warrior "Hunter" and when he discovers that "he" is a she, Lachlan couldn't be more stunned...or delighted! But no matter how lovely the lass is, he's seen her conferring with an enemy of his clan, and he doesn't trust her an inch. Especially when she takes a job as nursemaid to that enemy's young children. So Lachlan appoints himself her escort, refusing to leave her side—which makes for very interesting days...and nights!