You are absolutely wrong. Mexicana is a "flag carrier" for Mexico. It is every bit as soveriegn as a private flagged ship.
Under International Civil Aviation Organization (ICAO) regulations, of which Mexico and the US are signatories of course, the aircraft was Mexican "territory" even if it had already landed.
This woman was just 20 minutes shy of dropping her anchor baby where she wanted to.
Since the US has no fortitude, the mother and child will stay and soon be collecting thousands of dollars of your property tax money.
Think about it. What is this story truly about, then? Paleo, I know you keep the aviation ping list. Are you a pilot? From a pilot's perspective, a pilot of a U.S. flag carrier is most likely expected to enforce his or her version of U.S. law onboard (one couldn't expect otherwise). But in the eyes of the law, that does not make the carrier sovereign territory.