Hollie Robinson Marsh was just four years old when was pictured giggling in the arms of Princess Diana when the Royal visited a children's ward at Northwick Park Hospital in 1997.
After the Princess' death the photograph was used to illustrate a certificate for a £5 memorial coin.
Hollie recovered from the disease and had been so inspired by her meeting with Diana that she went on to work with children with autism and other difficulties at Kids Can Achieve in Harrow, London.
She was still working there when, on her 21st birthday, she had the shocking news that her cancer had returned – a one in a million chance, 17 years after the iconic photo was taken.
Hollie died after an intense dose of chemotherapy and radiotherapy caused multiple organ failure.
More than 400 people went to her funeral last week following her death in September.
Recalling the day, her daughter met the Princess, mum Claire, from Ruislip, told Mail Online: "To Hollie it wasn't a big thing, but Hollie was always that kind of person. You could introduce her to The Queen and she'd be the same way as she is with everyone.
"She just treated everyone the same. She was very natural with Princess Diana. Hollie was always just a very easy going child."
After the memorial coin was released, Hollie took that in her stride, too.
Claire, 46, said: "She was excited about it and over the years she was always happy to talk to other children and take her coins into school to show the class. It was always something that she looked at."
In an interview with The Times, Claire added: "Hollie remembered meeting the princess but not the details of the day. She didn't really mention it to people because she did not want to be different from anyone else."
She said when Hollie was diagnosed, she was upset that she'd lose all her hair again. Despite this, she was positive throughout.
She was told she'd need a bone marrow transplant and a successful match was found in her 18-year-old brother Jake.
However the chemotherapy she needed before the transplant led to organ failure and she died. Claire added: "Her friends said they couldn't believe how poorly she was because she never told them. I am grateful for the extra time with her. She was beautiful.
"Looking back on it now I can see she was put here for a reason. There was a reason why we had her for those extra 17 years. She was made to look after those children.
"It's inspiring in the fact that she met Princess Diana who loved children and Hollie went on to work with children with special needs. She was a remarkable person in that respect."
Simon Jarrett, the chair of Kids Can Achieve, said Hollie's death was a huge loss to both the staff she worked with and the children they care for.
He said: "We are terribly shocked and saddened by her death. She'd worked with us from the early days of our organisation. She is somebody who had gone through great trials herself and the gave up a career to work with children with very high levels of need.
"She was a great worker and friend and we'll all miss her greatly. It's a really shocking loss we've suffered."