Book East (East, #1) by Edith Pattou
Rose has always been different. Since the day she was born, it was clear she had a special fate. Her superstitious mother keeps the unusual circumstances of Rose's birth a secret, hoping to prevent her adventurous daughter from leaving home... but she can't suppress Rose's true nature forever. So when an enormous white bear shows up one cold autumn evening and asks teenage Rose to come away with it--in exchange for health and prosperity for her ailing family--she
readily agrees. Rose travels on the bear's broad back to a distant and empty castle, where she is nightly joined by a mysterious stranger. In discovering his identity, she loses her heart-- and finds her purpose--and realizes her journey has only just begun.