Lesley Keeley, from Allerton Bywater, was on a Thomas Cook flight from Marsa Alam to Birmingham Airport when one-year-old Nancy began to suffer convulsions and nose bleeds.
She and her partner had been celebrating Nancy's first birthday in the Egyptian resort and when the baby seemed off-colour on the journey home, they assumed she was teething.
"Her temperature started rocketing. At this point I started to panic as I had two hours left of the flight," said Lesley, 28, who works as a personal trainer.
Cabin crew gave the family Calpol, but Nancy's condition deteriorated.
"Then she started going all pale, unresponsive, nose bleeds and her eyes started rolling in the back of her head. At this point I started crying as fear really set in as I was on a plane with nowhere to go."
Seeing the baby's distress, an off-duty doctor who was a passenger on the flight stepped forward to treat Nancy.
"Words cannot explain how grateful I am to a lady who turned out to be a doctor. She saw what was happening and came to the rescue. If it wasn't for this lady my little girl probably wouldn't be here or she could've been left with brain damage. Nancy's temperature had got dangerously high and she was going to start having convulsions.
"I know as a doctor there is a duty to look after others, however she could have easily have sat there and not come forward. You also didn't have to stay with us until the paramedics arrived."
Nancy, who has since made a full recovery, was diagnosed with an acute virus when the plane landed.
The family only know that the doctor was called Jo and lives around 40 minutes from Birmingham. The flight was on January 22.
"Normally Nancy is a very good traveller - that was her fifth flight in six months," added Lesley.
If you are or know the doctor, the YEP can put you in touch with Lesley.