Certainly given the way Charles's life had gone (not being able to marry for true love, the behind the scenes stuff with Dianna etc). If he had been in that situation I think there would be a lot more sympathy towards him.
Like people above said, Dianna's death gave her, almost a pass for her behaviour, something I think she won't get in this timeline, especially if it comes out that her relationships took Charles to the brink. I don't see her acting like Fergie though since, lets face it, Dianna isn't a chav (Fergie probably is a bit). I think she'll certainly be involved a lot with charities and the sort. I could see her clashing a lot with the queen. I genuinly think she would want to be invovled in her children's lives as much as possible whilst the Queen will want to raise them (in particular, william) the royal way to ensure the line of succession is adhered to and in particular, so William becomes a good king.