Note that isn’t the only option. They can charter private planes. Still not publicly trackable as it isn’t public knowledge that a given tail number equals that celebrity.
Still, if it’s about environment, abstracting the flight to an odometer would suffice without stalkery implications. However I presume it’s not hard to get the tail number for a rando, and then they don’t need any help tracking her in particular, public flight tracking resources would do it. So while she might be able to fight a targeted tracker, probably the worst she has to fear would still be able to track her.
If I were anywhere vaguely in those shoes, I’d always use chartered private planes, limo services, etc. I would not move about in easily recognized and tracked personally owned transportation. Of course I’m not and definitely wouldn’t want to be flying much at all, but if I were in a position where I needed to fly, but couldn’t reasonably risk sitting among random folks, then chartering a flight seems a logical strategy.