The widow of famed fashion designer Oleg Cassini has been jailed for more than six weeks after refusing to follow court orders in the tortured legal battle over his $55 million fortune.

As the 68-year-old Marianne Nestor Cassini cools her designer heels in the clink, the Nassau County Public Administrator wants to force the sale of one of her Manhattan mansions to pay the numerous judgments against her in the estate case — including a nearly $51 million charge for her improper behavior as administrator of her husband’s affairs.

“Marianne’s malfeasance, misconduct and self-serving abuses” have been exposed, according to new Manhattan Supreme Court papers filed by the Public Administrator in the 12-year-old court fight, in which Marianne has successfully stalled for so long that Oleg’s daughters by actress Gene Tierney, Christina and Daria, both died without getting their rightful portion of his assets.

Oleg Cassini, who dressed Jackie Kennedy, died in 2006 at age 92. His grandson, to whom a court ruled Marianne owes more than $760,000, is also seeking to force the sale of 135 East 19th St., a four-story, $15 million townhouse.

Not even the iron bars of the Nassau County Correctional Facility have persuaded Marianne to loosen her steel grip on Oleg’s money and businesses, Oleg Cassini Inc. and Cassini Parfums Ltd., which were turned over to the control of a receiver in 2015 after Marianne and her sister, Peggy Nestor, were accused of mismanaging the companies, according to court papers.

“Nestor Cassini continues to use the companies to grab as much money for herself as she can,” receiver Rosalia Baiamonte wrote in a 2017 Nassau Surrogate Court filing.

Nassau Judge Margaret Reilly ordered Marianne’s arrest on May 3 for contempt of court for dodging requests to turn over business records and documents.

Handing over the documents would secure her release, but Marianne “apparently directed her minions to throw out . . . business records” after her arrest, according to a recent Nassau County Surrogate Court filing by attorney Robert Harper, who represents the executors in charge of Christina and Daria Cassini’s estates.

“Marianne has engaged in a pattern of obstructionist conduct the likes of which are rarely, if ever, seen in Surrogate’s Court,” Harper said in a legal filing.

Lawyers for Marianne Cassini didn’t respond to messages seeking comment.

Public records show Oleg Cassini Inc. is based in a Long Island manse at 313 McCouns Lane in Oyster Bay, but when ordered to turn over the keys to the court’s receiver, Marianne claimed the property was her personal residence, Harper wrote in the May legal filing.

She’s also long claimed 135 East 19th St. was her “primary residence” in a bid to stave off foreclosure after she used the home as collateral for a loan she failed to repay, according to court papers filed last year in Manhattan Supreme Court.

A person’s primary residence is typically protected from being sold to satisfy debts and judgments.