The Reiver (Medieval Outlaws) by Glynnis Campbell

A cattle-thieving Scottish lass chooses the wrong cow to steal and tangles with a laird who heals her heart and tames her wild ways. Raised by her abusive uncle, Cristy Moffat will do anything to impress her brawny cousins, including reiving the neighbor's cattle…until she steals the wrong cow and is caught in the act by the new laird. Brochan Macintosh has his hands full, repairing his tower house and raising his motherless twins. But when his plans to trade Cristy for his cattle go awry, he wonders if he wants to ransom her after all. Can he tame her wild ways and give her a family to love, and will Cristy be the one to heal his loneliness?