The socialite has now confirmed she is taking action against the royal couple and said the "case is really very difficult".
"I am now charged with a lawyer," she told the Mail. "They have a lawyer and I have mine too. What you read in the newspapers is really the reality of the case."
A source close to de Rouvre said her aggressive court action had "severely tarnished" her friendship with Prince Andrew and Sarah Ferguson, both now 60.
"Isabelle always loved having the Yorks to stay in their chalet and was particularly fond of their two children," the source said.
'So she was thrilled that the chalet, which has given her so many happy memories, was being bought by friends. Sadly this dispute has ruined everything. Isabelle is deeply upset that it has come to this.'
Born in Paris, de Rouvre was previously married to the colourful French businessman Cyril Bourlon de Rouvre. The couple are thought to have bought Chalet Helora during their marriage and enjoyed numerous skiing holidays there with their children.
After their divorce, de Rouvre became the sole owner of the property. She employed six full-time staff and rented it out for more than £22,000 a week.
Said to be decorated with chic antiques, the master bedroom is draped in animal furs, and there is a 60sq m indoor swimming pool, sauna, sun terrace, boot-room, bar and lavish entertaining area.
Neighbours include Sir Richard Branson and singer James Blunt.
De Rouvre is understood to still live in Verbier with Kennedy, who is in his late 60s and who dated Donald Trump's first wife Ivana in 2011.
The socialite's former husband became incredibly wealthy through tragic circumstances at the age of 33. He inherited his family's business empire when his father Evrard was stabbed to death by his valet in 1979.
Ten years later Mr de Rouvre, now 74, was elected mayor of Chaumont. In 1992 he used part of his fortune to buy the Ligier Formula 1 team for 200million francs.
His involvement lasted just one season and ended with him spending two months in prison after being accused of fraud. In 1999 he was convicted of tax evasion and was given a suspended sentence of 18 months.
In 2015, the Daily Mail exclusively revealed that Andrew and his ex-wife had secretly splashed out on the Swiss ski chalet. They bought the property as a "family investment", with the deeds listing them simply as Andrew York and Sarah Ferguson.
The chalet was split in two for the sale because, according to local regulations, it was too big for a sole foreign purchaser to buy outright. Legally, Andrew has the upper floor and attic space, Sarah the lower floor and basement.
Last night, a spokesman for the duke said: "This a private matter and the subject of legal dispute in which both parties are subject to a confidentiality agreement."
