It’s only about 8 hours. She literally has to show up and sit on the plane.
Maybe Camilla has a bit of fear of flying. Maybe she has circulatory issues that make long-haul flying difficult.
I have a fear of flying. Even in first class I'm miserable. I would be miserable on a private plane with every luxury imaginable. Because I would still in a metal tube 30,000 feet above the surface of the earth.