Interesting question, we are in England and my daughter was looking at US unis for a while, We seriously looked at 3 Scottish Unis (St Andrews, Glasgow and Stirling) and also considered 2 (Edinburgh, Aberdeen) - so sort of understand from the other way round, if that makes sense. I have been an academic for about 15 years, if that's relevant. FWIW BBB should give you a wide variety of choices in UK, many top 10 UK Unis want more, especially for the popular courses like Economics, but with a more niche subject like yours there should be some real quality unis to chose from
Lots of good stuff already said. English schools and Unis are different to Scottish schools and Unis, the latter is closer to US experience IMO because Scottish Highers (the exams there) are closer to US equivalent. Where as English A levels are slightly "higher" level and Uni year 1 can be tough to catch up / keep up in English Uni from US
UK also has regional unis that tend to have lower entry requirements and take more of their students from the local area (eg Sheffield Hallam. Oxford Brookes, Stirling and the post 92 Unis) while others have global reach and higher entry requirements (eg Uni of Sheffield, Uni of Oxford, Edinburgh)
The key with regional Unis is knowing the subjects they are really good at, and which of the "Top 10"s have more modest entry - a professional adviser should be able to help
Logistically, getting to some UK Unis is easier than others, not sure where you are in the US but international flights to UK can be a long way from major Uni towns. London has two main airports, Heathrow and Gatwick. And then you have Manchester, Newcastle, Birmingham, Glasgow, Edinburgh - have a look on Google Maps and you will see. And dont assume the roads / trains are great, for such a small country our transport infrastructure is rubbish. Something like Trainline would give you a sense of possible journeys / journey times
Stirling was a lovely campused Uni near a small town, grades were very modest (more a regional uni) but my daughter was concerned about studying with students who had got in with much lower grades than her (she was at AAB A*EPQ) they offered BCC for Economics / Politics (I think)
Uni of Edinburgh and Uni of Glasgow were both amazing city campus Unis, pretty high grades for most subjects, high cost of living. Both cities also have 2 (maybe more) regional unis with more modest entry requirements for many courses - again its important to know which subjects the regional unis are good at
Aberdeen was nice, but remote (both in getting there from US and going anywhere else nearby - its a bit of a bubble). Uni of Aberdeen has a sort of regional uni vibe in a good way, but great reputation in some subjects. There is also a regional Uni there I think (Robert Gordon?) dont know much about that one
St Andrews is unique, the uni is possibly bigger than the town (which is also Golf mad by the way) Reputation from some subjects is excellent, entry grades can be brutal. A lot of US folks go there, lots of money there, its not like any other uni town IMO
Dont know much about Dundee though I know someone who did medicine there and loved it. Again I think there is a regional uni in Dundee (Abertay)
A key question is why UK? And where does she want uni to take her? If this is more of a life experience than a career path then that would indicate different choices - eg I can imagine York being a great place to be, lots of history, mid sized campused uni. A little hard to get to (probably fly into Manchester, train to York). Likewise Glasgow / Edinburgh regional unis would be great for entry and "experience" but are not campused. All are expensive to live but you said that's ok.
BTW, not sure about Lancaster, my eldest has been having a very poor experience with 1 department there (she is doing a joint degree). Her sister is applying to Uni this year and was initially looking at the Lancaster for Biomed but decided on York and Warwick instead. It is also a bit remote from anything particularly interesting, except the Lake District 1 hour north and Manchester 1 hour south.