A 15-year old Australian girl who said she was groped on a flight from LA to Sydney has been told by the airline she "wore extremely short shorts" and had repeatedly climbed over another passenger.

Chelsea Schiffel alleges she was touched inappropriately by an elderly man on a United Airlines flight in July 2014 when she was returning home from a holiday with her family, News Corp reports.

Schiffel alleges during the course of the lengthy flight a man touched her breasts twice before she notified her mother Narelle.

Despite complaining to air crew and requesting alternative seating arrangements, the pair claimed they were asked to return to their same seats for the remainder of the flight.

A letter from United Airlines denied the pair's allegations, and implied her choice of clothing may have been to blame.

"Chelsea repeatedly moved in and out of her seat, crawling over the other customer who was attempting to sleep, and that your daughter wore extremely short shorts," the airline said in a letter, as sighted by News Corp.

"You have provided no evidence of any negligence on the part of United regarding this matter."

The family's attempts to take legal action against United Airlines has so far been hindered due to a lack of evidence.