Were you ever convinced you were adopted and no one had told you? I know a lot of people do at some point in their childhood. Maybe they saw a movie, read a book or heard a news story about a hidden adoption. Most likely the child either looks or thinks differently from the rest of the family. The fact that she looks or acts differently from the other people in her family makes her doubt her genetic connection to them.
When a child doubts her genetic connection to her family, it is usually a temporary phase of childhood. It doesn’t mean she loves her family any less or that she wants to leave. She is merely questioning her place in the family. Usually some photographs, a few family stories and sometimes a birth certificate will convince the child she really is genetically connected to the rest of the family.