Having been a teenage girl with an older and very immature brother with immature friends, I understand your concern. One friend used to drive his car with brother, me and a friend inside (no seat belts) and skid his 2cv around, handbrake turns. A car liable to flip btw. It was bloody frightening. Both he, my brother and his friend had crashes within a couple of years of passing their tests. Brother ended up upside down in a ditch. Drunk. His friend saw what happened, came to rescue him (also drunk) and put his car in the hedge just down the road. The other friend used to drive down the centre of the carriageway in a 60mph limit and carve out a third lane on a road, which could never accommodate 3 lanes - quite a few people did this back then. The speed limit these days is 40mph and it has diagonal hatching along the entire length of the road.
I'm not trying to say that this young man will act like this. The sort of really stupid driving I saw was an 80's phenomenon and policing is a lot stricter and the public much more likely to report driving to the police. I also think most young men are a bit more sensible these days too because they have had to pass a theory test so they know the rules, which will have created better knowledge and more respect of other drivers.
It is an hour away, which isn't that far. And he possibly won't yet have this stupid level of confidence I'm describing. This doesn't usually happen for a couple of weeks until someone learns the limits of the car and how to throw it around. I think instead of banning her, perhaps having a discussion about it would be a better way forward. Can you get the other parents involved? Talk to the friend? Or perhaps suggest that he takes her out for a drive somewhere in the next couple of days to see for herself what his driving is like. Tell her not to explain why she'd like to go for a spin. If he acts sensibly, you will be reassured and if not, then perhaps she will be put off.
She's 17 so it's a toughie to ban her especially as you won't be around. My dd isn't anywhere near this age but I think it is probably much better to give her the tools to protect herself as best she can and if you get her on side, she's much more likely to do it.