Rancher's Christmas Princess by Christine Rimmer

Arabella Bravo-Calabretti came to Elk Creek, Montana, with a secret to deliver and a job to do. Being a Bravo Royale, she was going to do it right. Before she handed her best friend’s darling son, Ben, over to his unwitting father, they would all spend Christmas together. Only then could she be absolutely sure that rancher Preston McCade was ready to be a dad.

Or...was that really the reason Belle was hanging around? She and Preston were practically from different planets, yet the attraction was undeniable. Before long, someone was utterly in love with a rancher — and Christmas in Montana was presenting one surprise after another.