We will always love you, Diana.
Why was she so special? I was young when she died.
She was doing what each new generation of Royals should do. Modernize the behavior of the institution of the monarchy. Not in revolutionary ways, but as manners change. It shouldn't be expected that an 80-something year old queen is going to change her ways. So Charles and Diana would start those changes in their behavior.
The problem arose because Charles was not allowed to marry the woman he loved, Camiila. Neither the institution of the monarchy nor the British public had come around to allowing him to marrying a married/divorced woman. So he had to settle for Diana. But the love wasn't there and Diana came to realize it and resented it.
Apparently Diana and the queen clashed. Perhaps Diana was more rebellious to the ways of the institution because she resented her marriage.
At Diana's death there was an outpouring of grief that surprised even the British public itself. I think a lot of that grief was based on the public's perception of her as wronged in marriage and by the queen. However, I feel the British public had a lot to do with the whole sorry marriage because of its attitude to allowing Charles to marry whom he will, while the public allowed divorce for themselves. They held Charles to a standard they themselves do not adher to, then blamed him when it failed.