I feel the author did a wonderful job of creating a character that I really did not like. Yes, Sybil had guilt and abandonment issues that were intensely sad .,, and tragic. For that I felt for her. She was kind to Harry and eventually kind to Theodore. She was kinder to Theodore when she needed him.
Writing such an unlikable character is a talent and I appreciated that.
I also appreciate the imagination to have the entire novel as letters and e-mails.. so creative.