I'm a new driver myself - rather newer than your friend. I'm an awful navigator, so I tend to put the satnav on and let it do the bulk of the thinking, but even so, in my couple of weeks on the road, I've learned that blindly following the satnav, you might as well be following the crazy man who sings about prime numbers on the bus and it's mostly useful for just pointing you in roughly the right direction.
So far it's tried to send me into a pedestrianised town center, has suggested I go the wrong way around roundabouts (when Dad accidentally set it to 'bicycle' mode), advised me to take roads that didn't exist or had been restricted to buses, and regularly loses me completely in Coventry, usually when I'm on one of the more terrifying roundabouts. In those cases I just take whichever exit it's safe to take around the other lost people who don't know which lane they need and let the damn thing have another guess. It quite often doesn't know there are roundabouts coming up, especially on major roads, but as I trust the thing about as far as I can throw the car, I'm always watching the road ahead and what other drivers are doing as well as looking out for road signs. Perhaps it helps that as I drive an old car, I know that if I had an accident like that, I'd not be likely to walk away from it.
However, having said that, there have been a few times, especially when I've been driving for over an hour and my passenger is an experienced driver, that I've nearly blindly obeyed an instruction from them before my brain catches up. I can see how it happens, but that's been sudden instructions such as 'next left' rather than carrying on going. I still think I would have known there was a roundabout coming up and not driven into it. And now that I've said that, I fully expect to have a really stupid crash in the next week or so.