So, Dalby to Condamine, to Surat to Roma, is about 330km - still less than a full tank of fuel. If that was her intended route, with no further deviations. I'm not sure about the tank sizes and fuel-to-km ratio of a Hilux, and have zero knowledge of diesel vehicles. However, I agree that fueling up in a big town, where prices are cheaper, is the best option. A trip of that length would likely not need a re-fueling.
There has been mention of the vehicle being a work vehicle and a work colleague using it. I have questions around this that I haven't found answers for, nor do I know if this is the truth. Who is the registered owner? (Registration has since lapsed) What is the boss/employee/colleague situation? Why was it borrowed, work or pleasure? What sort of work, as Tayla's current job - if she has one - is quite vague? If the vehicle did change hands at some point recently, where, when and how did this occur? On this note, after taking possession of the car, could it have been lower on fuel than anticipated and only noticed after leaving Dalby, requiring a pit stop to refuel at the nearest place?