Shes not written it to be the most beautifully written book. It's like a chatty diary/document remembering her childhood through to the now.
So take away your expectations of a well written book and place them with an insight to what it was like for her as a Spears in that world. She has nothing but respect for her sister throughout. It is all about what she went through and her perspective of experiences. It's very open minded, true and honest. I believe her.
