Leaving JFK with a French passport to enter Europe

My daughter is still waiting for her US passport and we both have dual citizenship (French / American). Travelling this Friday to Europe she will have to use her French passport. Delta on the phone said it's OK but on some websites I see that they may ask for both passports at check in and perhaps at customs leaving JFK?
Best Answer
I've never done it with Delta, but I do it all the time with European airlines. There is no routine customs or immigration inspection of departing passengers. There is an extremely remote possibility that CBP will do a spot check at the gate. I have never encountered one.
Pictures about "Leaving JFK with a French passport to enter Europe"



The Most Powerful European Passports 2020
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Anthony Beck, Mehmet Turgut Kirkgoz, Nataliya Vaitkevich, Czapp Árpád