Why does she want to go to college in the US? I think you need to get her to articulate this. Does she really know, or is it about California & the movies etc etc etc?
I suspect that there may be too many US teen films about college: the reality is rather different.
How independent is she? While my 1st year students are ahead of US Freshmen in knowledge terms, they are a long way behind in independence and resilience. (I've taught in both countries, btw). The UK A Level system is so spoonfed now, because of schools needing the league table wrecked education system blah blah blah ad infinitum
You can't drink in the US until you're 21
UK education is emphatically not expensive either in absolute terms or in comparison to a decent US college. The £9k fee doesn't quite cover the cost actually. A decent US college will cost a minimum of $20,000 pa for 4 years, plus accommodation, travel etc. No loans, and very little ability to do part-time work because of visa restrictions etc. And health care???
Also and I'm sure you've thought of this a UK university with a year abroad is the best way to get the US college experience, with guaranteed quality.
If she wants the variety of subjects (although I doubt she actually knows how the US college degree works) then a Scottish university is worth looking at: 4 years, and you start off with several subjects, narrowing it down in the last 2 years at Honours level.
Most US colleges require a broad range of subjects which go towards educatig to create rounded & broadly knowledgeable graduates. So there will be science, maths, stats, and language requirements, which will be compulsory. It's a wonderful system, but very different from the UK.