I remember reading that she found out somehow that he still loved Camilla and not her, but she went thru with the wedding anyway.
She was no saint, but I put most of the blame on Charles and the rest of the Royals. It was all politics and Diana was just a naive 19-year-old.
I read something of the sort too... that Diana had second thoughts, but her family told her it was "too late," all the preparations were made. I think it is just a sad story all around. I have to admit, however, that I lost a lot of sympathy for Diana after reading that at one point she tried to get Charles' attention back by throwing herself down the stairs... while pregnant. She was in a horrible situation, but to jeopardize your unborn child... of course, the rest of the story is that Charles wasn't too concerned about it. Hard to know what to believe, except I think for the most part, they've all lived somewhat miserable lives. High price to pay for the money, celebrity, possessions, etc....