Lets look at this from another perspective. Instead of AIDS, lets look at Polio. It wasn't until 1955 that Jonas Salk presented his first polio vaccine. Today, its among the WHOs most necessary vaccines. Although there have been outbreaks of polio as recently as 2013 in Syria, there really isn't much in the news about this disease. I'm sure in the past there have been spokespeople and fundraisers that spoke out on polio but I'd be hard pressed to be able to tell you who they are. What is amazing too is the list of well known personalities that contracted polio and survived and aren't generally known to the public. Franklin D. Roosevelt would be the one most commonly known but people like Alan Alda, Johnny Weismuller, Donald Sutherland, Judy Collins aren't well known. What history teaches us is that Jonas Salk invented the vaccine.
It will be the same with AIDS. Diana did stand up and speak up for AIDS and many of us here do remember it but AIDS also will follow the route of polio when it comes to history with hopefully a name added that has come up with a cure/vaccine against AIDS/HIV.
Diana, I don't think, will be singled out for her charity work as all of the British Royal Family does this. Its what was expected of them in that time frame and continues on in our present. What Diana did will have no more impact on history than what anyone else in the family has done. Perhaps if Diana had set up a Princess of Wales Research Center where the cure/vaccine would possibly be found, it would have more of an impact and she would have been remembered for that contribution but this didn't happen. Spokespeople and fundraisers call attention to causes and its the cause that is remembered, not the person when it comes to the annals of history.