

This system is called ADS-B. It’s a peer to peer communication between airplanes where each plane will share its own data (flight level, speed, coordinates, flight number, etc.) and data from other planes by broadcasting it on same frequency as others. Result of this is that all the planes know where other nearby planes are located and their heading thus providing additional safety in avoiding collisions and other issues.
Data being broadcast in all directions means us on the ground can listen to them as well, which is what some sites are doing. Add internet to that mixture and we have a world coverage of every plane on the planet. You might wonder why data is not encrypted or something similar. There’s nothing that can be abused about the data and all this tracking helps enormously with resolving incidents and other useful functionalities like precise arrival estimates and similar.
Now, since every airplane has a registration number, people figured out which plane was hers. Just like they know which plane Musk uses and many others. Data is recorded and known and completely legal, helpful even. If she has issues with this fact solution is rather simple. Get a charter flight or rent a plane and no one is the wiser. This is just rich people entitlement and the only way she can “win” this court case is to go a step further in stepping over the line which is to drown the poor man with legal expenses.
Edit: Oh, also location of boats is known. Not all boats, but commercial ones for sure. Their system is called AIS.
You are welcome. In order to receive this data one really doesn’t need a lot. Some USB SDR dongle around ~30$ and software which is readily available. It’s just like any other public service, free to listen to but license is needed to broadcast.