You are almost halfway there. Air-brakes are just a bit touchy so she should be careful when driving, but she has never driven a straight truck? If so, then try to borrow a friendly expeditor's truck at some truck stop on a weekend. You would need a mid-west location where you will find someone.
You can always rent a Budget or Enterprise truck- the main thing is to drive it, not the air brake part. Most important: learn the parts and how to do the walk-around inspection. The tester will ask what are you looking for and point to the headlight. (Answer: cracks in sealed beam, not just the bulb out). That is where most novices fail! I have a friend who knows driving, now needs a CDL, and virtually knows nothing about a truck.