Natasha Ednan-Laperouse, 15, collapsed on a British Airways flight from London to Nice on July 17 2016.
-> Girl with food allergies dies after eating Pret a Manger baguetteShe had been travelling with her father and best friend and stopped to get an artichoke, olive and tapenade baguette as they passed through Heathrow Airport's terminal five.
Unknown to the group, the sandwich dough contained sesame seed, a detail not mentioned on its packaging, according to a statement from her father, Nadim Ednan-Laperouse, read on the first day of her inquest at West London Coroner's Court.
Natasha was allergic to the ingredient and suffered a cardiac arrest despite two epipens being applied to her legs. She was declared dead the same day at a Nice hospital.
The family's lawyer, Jeremy Hyam QC, became emotional as he read Mr Ednan-Laperouse's statement to the inquest on Monday, at one stage pausing to regain composure.
Natasha at first felt her throat growing itchy and returned from the toilet with vicious red hives on her midriff, the inquest heard.
She was rushed to the cabin's toilets, where her father applied an epipen.
The statement said: "We waited a couple of minutes to see how she reacted.
"She said she couldn't breathe properly and it was was getting worse and urged me to get the second epipen right away."
He quickly jabbed the second epipen into her upper thigh, but it failed to relieve the symptoms.
"Natasha said that she still couldn't breathe and desperately looked at me, she said 'Daddy, help me, I can't breathe'."
She soon lost consciousness and cabin staff were aided by a junior doctor who had been on board in applying CPR for the remainder of the journey.
As hope began to fade that Natasha would survive in hospital, her father put a phone to her ear so her mother and brother could say goodbye.
Her mother Tanya could be seen wiping her eyes as she listened to the statement.
-> Leeds United fan and single dad, 46, paralysed from neck down after sudden heart attack"The pain and agony of the call was beyond anything I have known," the statement said of the moment Mr Ednan-Laperouse broke the news to Natasha's mother.
He then called his own mother and asked her to visit a branch of Pret a Manger in west London to examine the sandwich.
Finding nothing on the label or on the shelf, his mother made inquiries at the counter and was handed a folder of information.
"My mother looked down the list and found that the baguette dough had sesame seed inside it," the statement said.
"I was stunned that a big food company like Pret could mislabel a sandwich and this could cause my daughter to die."
Natasha had been travelling to Nice for a four-day break with her best friend at the start of what should have been "the best summer ever", her parents said in an earlier statement.
She was due to attend a youth Christian festival in Norfolk and go on a two-week family holiday to Greece during the summer months.
At the time of her death, Natasha had been working towards her GSCEs and hoped to pursue a career in law.
She also showed promise as a figure skater and loved horse riding, her family said.
The inquest heard on Monday that she had suffered from food allergies her entire life, but learnt to be diligent in scrutinising food labels and was alert to the danger of cross-contamination, the inquest heard.
Natasha put "her trust in food labelling", her father's statement said.
Antihistamines, epipens and inhalers had never before failed to halt an allergic reaction, it was heard.
The inquest continues.