Sure, with the wisdom of hindsight, it is easy to tell what were good decisions and what were bad. But I think there were few people in 1981 able to foresee that marrying the Prince of Wales was the worst choice Lady Diana made in her life.
anbrida, I remember when my father saw Diana walk down the aisle, he said, 'The Earl of Spencer must have rocks in his head. I'd never let my 19 year old daughter with no education and no experience go into something like this prince or no prince' She seemed too innocent, her husband didn't seem attracted to her type, and she was marrying into the most high profile and high stress marriage in the world where every little mistake and problem seemed magnified.
First people could see their age difference could be a factor in making the marriage go wrong: 13 years is a large age difference. In my own family, we have had one marriage with that age difference turn out successfully but we've seen several more marriages with similar age differences fail.
Secondly there was the purity you speak of: Diana was not only incredibly young, 19, but people remarked often that Diana cast an innocence and purity of being unspoiled, unsophisticated and untouched. Her father claimed that she had never had a lover and in her innocence she seemed far younger than her 19 years. Somebody that has that much purity and innocence often does not have enough life experiences to judge and act maturely and to make the best choices.
Thirdly, Diana was marrying into probably the most high profile marriage in the world. Charles' position as heir to the most well known monarch in the world meant his wife's position was going to be high profile and high pressure. Although not much was known about Diana's early life at that time, people knew a lot about Charles' life and previous relationships. It is possible for marriages with large age differences to work however, Charles had never had a history of being interested in women a lot younger than he was; he always was attracted to older women or women closer to his age and he didn't favor the romantic type of love but more of a sharing of deep friendship.
It is possible I suppose that Charles and Diana could have surprised us and that only knowing what we knew, Diana could have shown a strength and maturity that her innocence facade masked and Charles could have shown a romantic, dashing knight in shining armour side of him that we hadn't seen before, but the couple didn't show us anything to make us believe that their were any hidden strengths under what they showed us.
Whether Camilla is now seen as a winner is not clear. I will say that Camilla has one trait that in general make people's lives more rewarding and productive and that is that Camilla focuses on the relationships with those closest to her and manages to have mutually beneficial close relationships. I don't believe that Camilla is simplly lucky and that Diana was unlucky. I just think there is one trait that Camilla has that helps her with maintaining these close personal relationships and Diana didn't have this trait.
However compared to Diana, Sarah who made a lot of wrong choices can be seen to come out a winner. At least she is around to see her daughters grow up. Sarah made so many mistakes in her short life and she is not that good I think in really making her close relationships successful.
However, I think the difference between Sarah and Diana and the reason that Sarah is alive today despite her many many poor choices is that Sarah lacks the capacity for revenge. When one engages in revenge, a chain of events can start off which often comes back and destroy the original person. Also with Diana I think the type of people that her vengeful nature attracted, like Paul Burrell, and Mohammed al-Fayed were dangerous company for her to have around. In fact, I think that if Diana had been exactly the same except for one thing and if she had not had the capacity for revenge, I think that Diana's life would have turned out much differently and probably much happier for her and everyone around.
Sarah has not made good choices with her friends and companions either but her nature does not attract the dangerous users that were probably attracted by Diana's less attractive and more vengeful side.
I've heard separately that Diana was with Dodi that night she died to 1) make Hasnat Khan jealous 2) steal the thunder off of Camilla's 50th birthday party. Either way, she knowingly allied herself with the son of a man with dubious business connections and one who wanted to avenge himself on the British establishment who had cast him off.
And Diana willingly associated with the al-Fayeds for what? To make an old boyfriend jealous? Or to knock her ex-husband's love off the front page? This is one area where I believe that Diana's choices directly affected the short tenure of her life. That and her decision to not have security and tell the press that they were going to be surprised by the next thing she did. These were all incredibly bad choices that directly affected the way her life turned out and Charles and the Royal Family didn't have any influence over any of them.
So while many choices in her life were hard to judge at the time I think two: the first of her marriage and the last choices she made regarding her security and life with Dodi could be seen as bad choices at the time.