Her mother re-married. And THAT man is her dad to her. He's the one that changed her pull-ups, helped her with homework, kissed her good-night, and love her like she was his own. He is her dad to her in every sense of the word. She has no interest at all in knowing her birth dad. The fact that they share some genetics means nothing to her. As she puts it, "I share genetics with everyone on earth. My dad is the one who was there for me." And I really believe her. She's even refused to release her info to her birth dad.
She's a pretty "normal" young woman. There's nothing wrong with her for considering her adoptive father to be her father.