Margaret Findlay, the official joint-owner of 2008 Gold Cup winner Denman along with Paul Barber, died on Monday at the age of 86.
Findlay, mother to professional gambler Harry, was a popular figure in the industry and Denman, nicknamed The Tank, carried her purple silks to victory in the 2007 Royal & SunAlliance Chase.
Paul Nicholls, trainer of Denman, led the tributes, saying: "She was a lovely lady who I got to know back in the Denman days with Paul Barber and Harry. It's very sad for her family.
"Her enthusiasm for the game was what I remember most – she absolutely loved it. It is terribly sad."
Neil Harman, who wrote Harry Findlay's book Gambling For Life, confirmed the news in a tweet on Monday evening.
He said: "I first met Margaret about five years ago at Harry's box at Royal Ascot. She was a lovely lady and great company.
"She blamed herself for the way Harry turned out to be after she gave him another two quid after he'd run out of money on his first visit to the dogs, and of course that turned into eight pounds and so on."
"When she retired from her job as a nurse, Harry was quite troubled about how she would spend her retirement, but she used to go to the tracks in the West Country and the jockeys took her under their wing.
"The main thing to remember is how the racing community were warm and friendly in welcoming her into the sport late on in life. She loved watching her horses run and knowing they were hers was something deeply important to her."