She's said her delayed response is the biggest regret of her reign. It has been said that Queen Elizabeth's biggest regret is her response to the Aberfan mining disaster. The Crown season 3 depicts the Aberfan disaster and Queen Elizabeth's (Olivia Colman) reaction.

There’s a video on YouTube of her visit and she is clearly upset,” another remarked .

"Aberfan," the third episode of season 3, tells the story of a particularly horrifying day in U.K. history: The Aberfan mining disaster, which killed over 100 children at the Pantaglas Junior High School.
Here's why it took her eight days to visit, as depicted in 'The Crown' season 3. The Netflix series also attempts to explain why it took eight days for the queen to pay a … The tragedy in Aberfan would become one of the United Kingdom’s worst mining disasters—and it was completely avoidable.

Queen Elizabeth II and Prince Philip visit the coalmining village of Aberfan in South Wales, eight days after the disaster in which 116 children and 28 adults were killed It’s ridiculous how they portrayed the Queen as unfeeling during the Aberfan disaster.