Mellon's family and her longtime personal attorney said she died of natural causes at her beloved 4,000-acre Oak Spring Farms in Virginia's horse country, where she entertained royalty, stars and politicians but from which she rarely ventured.
Her death was confirmed by Alexander Forger, her personal attorney for the past 40 years, and her grandson Thomas Lloyd.
Mellon lived a closely guarded life dominated by the arts, fashion, horses, rare books and extraordinary gardens.
"She was involved in the business of nature and beauty, design and implementation," Forger said.
After spending most of her life trying to avoid the spotlight, she was thrust into it when Edwards was indicted in 2011 for using what prosecutors alleged was campaign money, including $750,000 from Mellon, to hide mistress Rielle Hunter and their child during Edwards's 2008 Democratic presidential bid. A jury later acquitted him on a campaign finance charge and deadlocked on five other felony counts. Mellon was not accused of breaking any laws.
Friends said Mellon should be remembered more for her contributions to the world of horticulture, art and fashion than the scandal that marked her last years.
"She's a remarkable person," said her friend, interior designer Bryan Huffman of North Carolina. "The last standing true American aristocrat."
Listerine HeiressRachel Lowe Lambert Lloyd Mellon's mother gave her the pet name, "Bunny," which stuck with her throughout her life, Huffman said.
Her grandfather, Jordan W. Lambert, created Listerine. Her father, Gerald Lambert, built a company that made everything from Dentyne to Schick razors before it was sold to Pfizer for $110 billion in 2000.
In 1932, she married Stacy Barcroft Lloyd Jr., a businessman and horse breeder. After their divorce, she married his friend Paul Mellon - at the time, reportedly, the world's richest man. Paul Mellon, a renowned art collector, philanthropist and thoroughbred breeder, died in 1999 at age 91.
Huffman, who introduced Mellon to Edwards, said the former presidential candidate reminded her of John Kennedy.
"She liked what he said about the 'Two Americas,' " Huffman said. "She believed deeply in what he was saying."
Edwards aide Andrew Young, who wrote about Mellon and Edwards' relationship in his tell-all book "The Politician," said Mellon became so distraught when the media attacked Edwards over a $400 haircut that she sent him a letter offering to help. Mellon eventually gave Edwards more than $6 million, Young said.
He said Mellon wrote in her letter, "... from now on, all haircuts, etc. that are necessary and important for his campaign - please send the bills to me ... It is a way to help our friend without government restrictions."
Young described how the campaign used the so-called Bunny Money to hide Hunter. Mellon sent checks to Huffman inside boxes of chocolate, and Huffman would direct them to the campaign, Young wrote. Mellon's attorney said she had no idea the money was going to hide a mistress.
"She was not looking for an ambassadorial" appointment, Huffman said. "She has always cared greatly beyond herself."
Her grandson, Lloyd, said, "I think she was trying to help (Edwards) for the right reasons, believed in him, and I think frankly he just took advantage of a lot of opportunities that she gave him."
Huffman said his friend remained in good spirits despite the Edwards distraction. She had endured worse, including the 2008 death of her daughter Eliza, who had been left quadriplegic when hit by a car years earlier. She had a son, Stacy Barcroft Lloyd III, and two step-children, Timothy Mellon and Catherine Warner. The daughter was married to former U.S. Sen. John Warner.
Mellon was a "legend in design and gardening circles" who had a low-key style that was eloquent but unpretentious, Huffman said.
"She's not sitting around in velvet-covered gold chairs. That's the antithesis of what her style would be," he said. "She is without the trappings someone would associate with an heiress."
When she was around 5 years old, her father let her have a little garden at home, planting the seed for her lifelong love of horticulture, he said.
A self-taught botanist, Mellon was tapped by her friend Jacqueline Kennedy to design the White House Rose Garden. She created another White House garden that was named in honor of Kennedy after her death. Mellon's Oak Spring Garden Library, which houses her collection of rare books, manuscripts, works of art and other pieces relating to her hobbies, is one of the largest repositories of horticultural information and is visited by scholars worldwide.
Mellon also was known for her exquisite taste – both in fashion and in decorating.
Her wardrobe was created by Spanish designer Cristóbal Balenciaga until he retired, at which time French designer Hubert de Givenchy took over fashioning everything she wore, according to a 2010 Vanity Fair article.
Her art collection included a Rothko reportedly worth $125 million.
Donated Project Hope HeadquartersMellon spent some of her childhood at Carter Hall, an 18th century mansion in Virginia's Shenandoah Valley. A donation from Mellon in 1977 helped make the home the headquarters for Project Hope, the worldwide medical outreach organization.
She attended Foxcroft, a northern Virginia boarding school.
She and Paul Mellon supported many philanthropic endeavors, but were also known to indulge. They reportedly had homes in Antigua, Paris, New York, Washington, Nantucket and Cape Cod, and a mile-long runway for their private jet. They were friends with the Kennedys and entertained Queen Elizabeth and Prince Charles. Until she neared 100 she practiced pilates daily, which she learned from the master Joseph Pilates in the 1950s.
Through it all, she never sought publicity. Mellon believed a lady's name should only appear in the newspaper three times: for her debut, her marriage and her obituary, Huffman said.