Léone Meyer vividly remembers the first time she saw her father’s cherished painting — Bergère rentrant des moutons (‘Shepherdess Bringing in Sheep’) by the Impressionist painter Camille Pissarro — in the basement of the Musée d’Orsay in Paris.

It was four years ago, and the painting, which had been looted by the Nazis during the second world war from her Jewish adoptive parents, had finally been returned to France by a museum in Oklahoma.

“The tears came into my eyes,” said Ms Meyer, now 81. “I almost saw the silhouette of my parents before me.”

Nearly 80 years after her biological mother, brother, aunt and grandmother were deported and murdered at Auschwitz, the Nazi concentration camp in occupied Poland, Ms Meyer has found herself embroiled in the continuing struggle to locate and return looted works of art traded around the world after the war.

Two court battles are now under way over the fate of her Pissarro. The court cases in France and the US centre on an unusual agreement struck in 2016 between Ms Meyer and the University of Oklahoma, which previously had the painting on display at its Fred Jones Jr Museum of Art.

In Paris, Ms Meyer is challenging the validity of the deal, which accepted her as the rightful owner but required a rotation of the painting every three years from 2021 between France and Oklahoma in perpetuity. The court’s reasoning was that the Fred Jones museum had been gifted the painting by an owner who bought it in good faith from a New York gallery without knowing it was Nazi war spoil.

Ms Meyer wanted to give the painting to the Musée d’Orsay, but it refused the bequest because it is not allowed to take on perpetual obligations to pay for regular transport overseas. The risk now is that by failing to donate the work of art to an institution in France under the terms of the deal, she will be obliged to hand it to the US state department for its Art in Embassies programme.

“Why don’t they just give it to her? She’s in her eighties and a Holocaust survivor,” said her lawyer, Ron Soffer. “Many museums in the world would say, ‘Here, you can have it’. For her it’s a matter of principle.”

Ms Meyer worked as a paediatrician but is also a retail heiress rich enough to buy Impressionist paintings if she wants to.

The painting belonged to Ms Meyer’s adoptive father, Raoul Meyer, a businessman who joined the French resistance and ran the Galeries Lafayette shopping empire after the war. He was also a musician and art lover who was “very attached” to his small collection of paintings, she said.

The Meyers had hidden their works of art in a safe at a bank in south-western France in 1940, but the Nazis seized the collection and sent it to Switzerland after the Allied landings in 1944. The painting was one of about 100,000 works of art looted from Jews in France during the German occupation.

It holds particular significance to Ms Meyer because of the painting’s importance to her adoptive parents, a couple who brought her into their family at the age of seven from a Jewish orphanage outside Paris in 1946.

“It’s about respecting the memory of my parents, a desire for justice, and the idea that this period allowed the killing of millions of people in the camps, including my biological family,” she said.

A court in Oklahoma, meanwhile, has ordered Ms Meyer to abide by the 2016 deal, which was validated by US and French courts, and to abandon the legal proceedings in France or be held in contempt of court in the US.

“At the end of the day what the [Oklahoma] museum wants is to have the painting on the wall,” says Olivier de Baecque, the university’s lawyer in Paris. “Mrs Meyer should respect the decisions of the justice system . . . The essence of a settlement is for the parties to make concessions.

“When you do a deal like that you need to compromise and if you don’t respect such compromises then there will be no deals in looted art cases.”

Pissarro’s representation of the shepherdess opening a farmyard gate to her sheep, painted in 1886, has had a typically roundabout postwar journey back to France since the war.

Raoul Meyer located it in Switzerland but lost a court case there in 1953 when he tried to reclaim it. It was later acquired by New York art dealer David Findlay, who sold it to a family that gifted it to the Fred Jones museum 20 years ago. Ms Meyer located it there in 2012 and began the process of reclaiming it.

It was only after the so-called Washington Conference in 1998 called for art looted by the Nazis to be identified and ownership resolved that the art world began to look more closely at the issue, said Mr Soffer.

“That’s when people started paying attention to provenance, and people started doing due diligence,” he said. “If they [the museum in Oklahoma] had done due diligence they would have been alerted to the fact that the painting is on the French government list of art looted by the Nazis.”

Michel Jeannoutot, president of the CIVS, a French commission to indemnify victims of anti-Semitic looting during the occupation of France, said there was “a general movement in Europe and in the US as well to have ‘clean’ museums, in which works of art are exhibited that have clear provenance”.

As she awaits the judgment of the two courts, Ms Meyer says her wish remains to give the painting in full to the Musée d’Orsay, which specialises in Impressionism and has similar rural images by Pissarro in its collection.

“This painting has been wandering around the world for nearly a century,” she said. “It should stop. It’s very important that this painting returns here.”