Diana cried several time in public. Not often, when you look at all the times she was photographed. 

Diana did break down in tears when she left Ashworth Hospital in Liverpool. Diana also broke down crying at a polo match where she watched Prince Charles played, and the paparazzi would not leave her alone.

On 29, March, 1981, Lady Diana cried after Prince Charles left on a five week trip to Australia, but Diana was sad about Camilla calling Charles right before he left.

Also, when Princess Diana’s father passed away, she cried in her car. That was in 1992. Not the greatest year for the princess.