She was thinking about some things in her mind.
She initially thought that her previous conjectures and feelings were wrong, as if she was overthinking things.
However, after an unexpected encounter with Frank Parker on the plane again, she finally realized that some things might not have been her misperceptions.
It's already very coincidental for one or two incidents to be mere chance events.
She really didn't believe that meeting Frank on the plane this time would be just a coincidence.
There are not so many coincidences in the world.
Even if they happened to be going to the same city by chance, it is still challenging to get on the same plane by coincidence.
And even if they coincidentally got on the same plane, could their seats be next to each other, coincidentally?
So, there is only one most probable possibility.
That is, Frank knew her itinerary and then bought a plane ticket for the same flight.
As for why he would do this...