Polly wants, there are lots of biographies out there if you want to find out more, (her brother Christopher's book is good). Short version, mother died of breast cancer when she was 5, new step mum and her didn't get on, strict Catholic upbringing, attention seeking, looking for someone to love her, being wary of people who may just want to use her for her fame/money/power. Abusive marriage, afraid of getting cancer (see mums death), dietary restrictions, excessive workouts, not being able to relax.
She is a full complex personality and has many sides the public don't see.