What does the relationship statement, "Her mother is the only girl child of your father" imply about the relationship?

The relationship statement "Her mother is the only girl child of your father" indicates that the person's father has one daughter, who is the mother of the person in question. This means that the person is the child of the mother, making her the daughter. Since the focus is on the mother being the "only girl child" of your father, it directly implies that the person is the niece of your father—since your father is the grandfather of her. This family relationship establishes her as a niece, which is why this option is the correct interpretation of the statement.