Ms Chauhan says she arrived at the airport at 12:20 PM local time, 10 minutes after boarding was due to commence.
Her digital boarding pass, seen by BBC News, shows her assigned to economy class seat 36G.
But despite having checked in online, she says airline staff would not allow her to complete the process at the airport.
She had travelled from Ankleshwar – 201km (125 miles) south of Ahmedabad – before being held up in Ahmedabad's city centre traffic.
Ms Chauhan says: "When I missed the flight, I was dejected. Only thing that I had in mind was, 'If I had started a little early, I would have boarded the plane'.
"I requested airline staff to allow me inside as I am only 10 minutes [late]. I told them that I am the last passenger and so please allow me to board the plane, but they did not allow me."
The Gatwick flight took off as scheduled on Thursday afternoon, but appeared to struggle to gain altitude and crashed about 30 seconds into the flight.
The plane hit a residential area, killing 241 passengers and 12 crew members. At least eight people on the ground are so far known to have died.
One passenger, British national Vishwashkumar Ramesh, survived the crash and was treated in hospital for injuries.
Indian, Portuguese and Canadian nationals were also on board.
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Among the 53 Britons to have been killed were a family who lived in Gloucester, three members of the same family who lived in London, and a married couple who ran a spiritual wellness centre in the capital.
Emergency services and officials worked late into Thursday night and into Friday to clear debris and search for answers.
