The child can have a relationship with both the real father and the step-father. There doesn't have to be a one or the other decision. Your child may feel if she opens her life to her father that she is disloyal to the step dad.

You may accidentally be affirming that idea. 12 year olds are quite adept at overhearing "grown-up" conversations, yet not seeming to be able to hear when you call them to do their chores. Be careful what you say about her biological dad, when she is in the house.

Your daughter is probably scared of a man she has only heard about, and doesn't know well. Encourage her to go to her counselor to work through these fears. A child should always be encouraged to have a relationship with their biological parents unless the parents might harm the child. You didn't indicated that you thought that was the case.