[Galadriel55]

I think that both Elmo and Pitch are right. If Nellas represents goodness, and she affected Turin's childhood, it makes sense that she also represents innocence and freedom in Turin's life (I mean inner freedom; when the curse did not have as uch power over him). When he lost innocence, he lost peace, home, and many other good virtues and values. When he separated from Nellas his actions begun to turn out for the worse. Nellas tried to come back to Turin, and she was always near him, hiding in the trees, when he was in Doriath. Turin could not, or chose not to see her, as he failed to see such things for the rest of his life. Perhaps if only he would remember her and search for her before he left Doriath, Morgoth's curse would have lost its power.
Pitchwife looks at it from a logical point of view, and Elmo more from a symbolical one, and I agree with both.