“She has to go through customs when traveling internationally (legally). So they DO know what country she is in.”
At Gatwick Airport in 2016, I had to fill out a card and talk to an official, after standing in line for over one hour.
The UK didn’t have a computer record of my entry, at least right away.
In France, they electronically scanned my passport and handed it back to me. No questions were asked and there was no delay.
She might be in Ireland, which doesn’t extradite to the US normally. Such residence would imply that she thought she did something illegal.
She’d go through the short UK/EU line at Gatwick.
I think foreigners have to give their airline their passport number (which is then given to the DHS) when taking a flight in US airspace.
She might have flown from Canada to the EU.