Huis clos question

Help!!! I'm looking for a novel where the heroine and her two brothers are on the run from a rogue wolf that killed their parent. The heroine is blessed because she can draw symbols pray on them and bring peace or protection. The heroine and her brothers seek refuge in a werewolf castle where the king's hand falls for her. I remember that the rogue wolf could also posses people. I would really appreciate the help