Yeah I think the vast majority of airport security is definitely security theater. Based on the fact she wasn’t caught until mid flight, you’re exactly right that getting past security and getting through the gate onto the plane wasn’t a challenge. Honestly I’m curious how they caught her while she was on board. I feel like if she had found a quiet empty window seat and pretended to sleep the whole flight she wouldn’t have been discovered. But maybe economy was full and she tried to sneak her way into first class or something

Edit: From the original article about her sneaking aboard

The flight was not sold out, and she was discovered when a flight attendant became concerned that the woman was making frequent and lengthy visits to various lavatories aboard the Boeing 767-400ER, according to a source familiar with the incident.

So yeah, she was dumb and bounced around the plane a bunch making the flight attendants look up who she was. My comment rings true