What was so special about Princess Diana?

On the radio they said that today marks the 25th anniversary of her death. Firstly, if she was so great, why mark the day of her death instead of the day of her birth, even if her death was rather dramatic? I have nothing against her. She was fairly attractive, and I felt sorry for how she was treated by Prince Charles and by how she was hounded by paparazzi, but what did she do to merit our attention?