Who is The Blonde from Sybil and what is their importance?

The blonde appears near the end of the book before Sybil's final integration. She has been with Sybil all along, and she is who Sybil wants to be. Sybil dreamed of being a vivacious blonde, as is her mind she believed this would make her more likable and lovable. The blonde is the adolescence that Sybil never had.