The airline said the child, travelling without a ticket, was discovered on board the flight on Monday night "hidden inside a bag".
A source at Charles de Gaulle Airport said the woman was a resident of France in the process of adopting the child, who was from Haiti.
"She was apparently in the transit zone in Istanbul, and had crossed the customs checkpoint with the child, when she was prevented from boarding a flight with her," said the source.
The woman then "decided to hide the child in a bag to get aboard another flight, after buying a new ticket. "Once on board, she placed the child at her feet, under a blanket, but the girl needed to go to the toilet and was noticed by other passengers," the source added.
Air France said it notified French authorities and the woman was taken into custody upon landing, but prosecutors decided not to press charges.
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She and the girl were however being held at the airport while authorities investigate the case.