People have seemingly completely overlooked the fact that the car was booked in with interior rattles

.
Two road tests are the absolute bare minimum for rattles. One to determine that there is actually rattle and roughly where you think it is coming from and the second after the work has been carried out to confirm that you've actually eliminated it - In many/most cases you need a lot more than just those two tests because more often than not the simplest explanation isn't the correct one (and thus why 99% of techs will say they hate rattles more than any other job).
Charging her twice isn't a blatant attempt of them shafting the customer. This isn't a "quality roadtest", it is diagnostic time, often requiring two members of staff (one driving, one listening/checking panels and trim). And in most cases it isn't a matter of taking it for a spin around the block for 10 minutes. Some rattles can only be heard over certain road surfaces, at certain speeds, with certain weight/loads in certain places.
Even though the road surfaces around our workshop are junk rattles always seem to become apparently on a certain road about 10 minutes drive away. So that's 10 minutes to get there, maybe 5-10 minutes of driving up and down this road with an assistant trying to pin point the noise and checking trim and then 10 minutes to get back to the workshop... Then you've got to repeat pretty much all of that again to confirm that the noise has actually gone. And that's if the job goes well.