the revolutionary princess
What made Diana unique is that she wasn't content to sit on her butt and give the media the opportunity the chance to trash her image and mock her. Before then we had to deal with "It's a Royal Knockout" and the Tabloids stories about "Randy Andy". Our Monarchy was not being taken seriously and nobody in power really seemed to care too much about it.
Diana understood how to create a largely positive public image and connecting with people by taking on humanitarian issues and actually engaging with those less fortunate even hugging them. Compare this with the depiction the establishment got in "The Queen" and Diana appeared to be truly innovative