How one "horrible" mistake caused a woman to fly 4800km in the wrong direction.

Lucie Bahetoukilae had booked what was supposed to be a seven-and-a-half hour flight from New Jersey’s Newark Airport to Paris’ Charles de Gaulle.

Instead, she endured a 28-hour ordeal which involved her being flown more than 4,800 kilometres in the entirely opposite direction.

Lucie, who speaks French, was mistakenly allowed onto the wrong flight after a last-minute gate change at the airport.

Speaking with ABC News 7, her niece – who translated on behalf of her aunt – said Lucie’s ticket was scanned at the gate printed on her boarding pass and she was allowed onto the plane.

“When she went to sit [in her assigned seat, 22C], someone was sitting there already,” Diane Miantsoko explained.

Instead of questioning Lucie's boarding pass - which read "Newark to Charles de Gaulle" - she was moved to an empty seat.

It wasn't until Lucie's flight landed in San Francisco, instead of Paris, that she realised there had been a mistake.

"If they would have made the announcement in French, she would she have moved gates. Of course, because she speaks French she would've moved to another gate," Diane said.

After being flown more than 4,800 kilometres in the wrong direction, Lucie then had to endure an 11-hour layover in San Francisco before she could be booked on a flight to her intended destination.

By the time she arrived home in France, she had been travelling for more than 28 hours.

Lucie and her family wanted to share the story not to gain a refund - although Lucie was contacted by United and given a full refund, and a voucher for further travel after her story went public - but to raise awareness of what had gone so terribly wrong.

"This is not about money, this is about United getting serious with their employees," Diane said.

"My aunt could have been anybody. She could have been a terrorist."

United Airlines has taken the blame for the incident, telling ABC 7 it "mistakenly put [Lucie] on the wrong flight", calling the incident "a horrible failure".

The airline added it was working with its employees at Newark airport to ensure the incident would never be repeated.

The airline has experience a run of bad press in recent weeks, after a passenger was forcefully removed from an overbooked flight in early April.