Well no, it isn’t an exception is it? “Birthright citizenship” in general is a legal fiction fairy tale. That’s how it’s supposed to work. Citizens of another country (like diplomats) are foreign nationals. An illegal alien isn’t a US citizen either.
This chick, for her part, is more or less an unlawful enemy combatant, and could be executed without benefit of even a trial. That’s how it’s supposed to work. Does she still want to come back?
Oops.
IIRC the Federal courts have consistently upheld the concept of “birthright citizenship”. IIRC it’s connected somehow to the 14th Amendment.