The US teens do not drink in the same unabated way as Brit teens do, not publically. I am not sure when and where they do their drinking but the type of drinking that goes on in the UK, it is a very British cultural thing you just do not get in the US and the friend is seeing that and rejecting it. Yeah she may be better just staying put in Boston as it will rub off on her teens Chiweenie
This is an interesting point. I first went to the US aged 18 (almost 19) to do Camp America. I had finished 2nd year of university (Scottish system- we can do it young!) and was relatively worldly wise - I had inter-railed round Europe for a month the summer before totally independently, had travelled widely, and was generally street wise growing up in a big city and at university in the same city.
Camp was a great experience, but I found the US staff very, very young for their age. They definitely has fewer life experiences than us brits- more sheltered somehow. They were, without exception, middle class, but this is the demographic OP's friend is coming from. Obviously they can't drink until they're 21, they did drink in the staff clubhouse (big fridges to buy and drink your own) but it tended to be light beer, and few drunk spirits. There were drinking games which were rowdy, and some got drunk, but it tended to be the alpha jocks only. They smoked a lot of weed though- there seemed to be a real 'we're being rebels ' vibe about that, which I just didn't get.
They were also, in general, Conservative: some thought I was a boy when I arrived as, shock horror, I had short hair; they all dressed very conservatively and couldn't understand some of our funkier dress choices (usual student stuff, not revealing); they were obsessed with girls being 'pretty'(being thin was everything) and boys being 'handsome and muscular'; they avoided debates about anything remotely political/ intellectual(I am a dyed in the wool socialist and was v active in student politics 🙈); LGBTQ+ rights/ people were kept at arm's length; very few were into cool music/ books/ films/ culture. It was generally very sanitised.
If OP's family is coming to the UK with a similar background/ mindset they will find it jarring. It's up to them. UK culture has a lot to offer if they can accept the odd bit of anti-social behaviour.
I agree with Autumniscoming - it won't rub off on the children I you don't want it to. It's all about what is taught/ happens in the home. I have 2 teens- neither of whom act anything like this and have varied, cultural lives and a wide variety of friends.