Kocharik Tsamouzian wanted to go to the loo shortly after boarding the plane but was told she had to remain in her seat for safety reasons.
See also: British Airways passengers complain of 'no food or loo roll'
See also: Man with valid passport refused boarding on BA flight to wedding
As she pleaded with staff a flight attendant even blocked her in the middle of the aisle.
The flight from Los Angeles to London was delayed on the tarmac for 90 minutes and Mrs Tsamouzian eventually wet herself, leaving her humiliated and in tears on the long-haul flight.
Kocharik Tsamouzian wasn't allowed to use the loo before take-off
The pensioner was not carrying a change of clothes in her hand luggage and was forced to sit in her soiled outfit.
Her daughter Aida Behroozi, of west London, told The Daily Mail: "I went to pick my mother up from Heathrow Airport and she arrived in tears.
"I was shaking with anger. She asked the air hostess over and over again if she could go to the loo but they kept telling her no because of health and safety reasons.
"My mother was saying, 'I'm an old lady you have to let me go', but the air hostess stood in front of her seat blocking her from getting up."
Mrs Behroozi said BA hasn't offered a proper apology or compensation to her mother.
She has vowed to never use the airline again.
A BA spokeswoman said: "We have been in touch with our customer after what we understand must have been a very distressing experience.
"Our highly trained cabin crew always work to make our customers as comfortable as possible, but Civil Aviation Authority safety rules stipulate everyone must remain seated with their seatbelts on after the aircraft has started moving.
"The safety and security of our customers is always our top priority."
The Heathrow-based airline has faced complaints recently after scrapping complimentary drinks and snacks on short-haul flights.
Passengers can now buy M&S snacks instead.
Earlier this month it was reported that BA is facing a £290,000 compensation bill after a flight was delayed because there 'wasn't enough toilet paper on board'.