I have a suggestion, if you two are having trouble getting the two to interact and develop a healthy relationship.
Let's say that the guest-room door Clare didn't check was locked. And in that locked room? A zombie? Be it one of her dogs, a parent, or a stranger, it was locked inside to keep it from attacking. Once it smells Clare it could start acting up and bust out, chasing her, an already smelly, odd looking bloody corpse.
Marco, being the good Samaritan he is, either breaks in or tries to yell for her to get her to open the door. Between a strange man and a shambling corpse trying to eat her face, Clare might be finally swayed to allow the lesser of the two evils inside. When h deals with the zombie, he could grab her by the arm, maybe bear hug her until she calms her business. He could give her a bit of food, knowing she won't trust him so easily, and focus first on asking what she knows, and maybe try to explain.