If your ladyfriend is afraid to drive it, she sure as heck is not going to be able to "steer it to safety" should you die at the wheel. I know with AAA's, they have to wait till they are at a certain point before they will fix them, but you need to have a heart to heart talk with your doctor about getting it fixed if that is possible.
My husband has a serious heart condition and he quit driving the big rig when he thought his condition could interfere with the safe driving of the vehicle. I now do all the driving of our 40' Class A towing our Flex. He drives the cars and our small B+ motorhome. Those would all be easier to manage if he should have an incidence driving.
So my advice is to go to something smaller she can handle easier and wouldn't be afraid to take over.
Also, you are misinformed about the air brake. The manufacturers tell you to reach over the driver and pull the air brake in an emergency. It will slow the rig down gradually and allow a person to take control. It would be scary for sure, but that is what they say.
Dale