I have the book, and it's quite a window into her world. She was truly amazing. I don't know if I'd say she was terribly insecure but yes she was a little. As her son describes it, towards the later part of her life, after she began work as a goodwill ambassador for UNICEF, especially after her first visit to Somalia, he says she became very sad.
Here's a passage from the book about it:
My Mother had a secret.
I don't think she would mind my saying it. We see things much more clearly...after. So here it is, the great secret.
She was sad.
Not that life treated her badly, and therefore she was sad. Life was tough but good. My mother was sad because of what she saw happening to the children of this world. I think we all made her a little bit sad. Yes, you did as well as I. Not because we were bad, but because we couldn't help. If she hadn't done her work for UNICEF at the end of her life, I wouldn't be so sure. I've done some work for the children, and I'm sad too. So this book will have to be about this as well: sadness and children. Not a great combination, but there you have it. I think if you got the whole picture, you would be sad too. So I'm not going to do that, I'll spare you the whole picture about the sadness and the children. But I'll give you a little bit of it, just enough.
Don't worry you'll smile as well. A smile is the perfection of laughter. And you may cry a little too. But crying is good for you eyes and for your soul. It beautifies.