After trying to engage a conversation with the pair and noticing that the man was quite defensive, Fedrick left a note in the airplane bathroom for the teenage girl to read. The girl replied to the note asking for help.
Fedrick then told the pilot about the situation and the police was waiting for them upon landing.
You may think that Sheila Fedrick is an incredibly astute observer, but there’s more to it than just instinct. Fedrick was trained by Airline Ambassadors to spot signs of human trafficking. According to Global Citizen, “thanks to the work of charities like Airline Ambassadors and flight attendants like Fedrick, 2,000 human traffickers were arrested and 400 victims identified by U.S. Immigration and Customs Enforcement in 2016.”
Fedrick is still in touch with the girl she rescued and says the teenager is now attending college. 
H/T: Global Citizen.