There are two issues here. The first is that you’re paying a lease on a vehicle that isn’t functioning right now. There’s not much that anybody can do about that and it’s not really anybody’s fault. The disaster that is current global supply chains has meant that freight out of the United States is either moving at snail’s pace or not moving at all. Many Australians are waiting for bits and pieces from North America, all of which seem to be stranded on the dock in the US. Perhaps you could talk to your finance company about some interest-rate relief, but based on past experience, I wouldn’t be holding my breath there. And since it’s not Jeep’s fault that global trade is in such a state right now, I don’t think you’d do much good there, either. Nor is this a Jeep-specific problem; many car brands are having trouble sourcing repair and service parts.
As for the vehicle being replaced, on the face of it, I doubt that you have much of a case. If Jeep refuses to or cannot repair the vehicle, then you’d have grounds for a refund or replacement, but if Jeep believes that replacing the engine will fix the problem, then consumer law allows for that to happen.
The chances of the same vehicle having two engine failures seems pretty slim, so I wouldn’t be worried about it happening again. Don’t forget that there are any number of reasons (fuel pump, sensor, electrical problem, fuse, relay and a thousand more) for an engine to stop virtually in its tracks. Again, this is not a Jeep thing; all car-makers have experienced engines that for whatever reason have simple spluttered to a stop, often at speed on the highway.
When that happens, of course, you can lose the assistance to the power-steering and the braking system which is what your wife is concerned about. But it’s probably worth explaining that even though she would have to wrench the steering wheel with lots of muscle and really stomp on the brake pedal, even if the engine stops, she would still have brakes and steering. They just won’t be power-assisted. And even if she doesn’t think she’d be able to turn the wheel if that happened, adrenalin is a very powerful force on its own in such situations. And, again, the same thing could happen in any make or model of car.