I went to a USA University for a year abroad, University California Berkley, as part of my first degree at Edinburgh University (which gets respect, I got a masters, a PhD place easily, went to Columbia as a graduate student).
For my exchange year I paid, zero. It is the same cost as fees at home university.
I loved it and honestly because of that I would have preferred the whole degree there, but as others have said, the cost is insane. It was a bit tough to leave after the year, but I think I took it harder than most!
So maybe look into UK universities that have international exchange programmes?
Also for a broader programme, definitely somewhere like Edinburgh. She'll get an MA as standard, (mine was an MSci, we had the choice to take on the extra work and higher level, but I think with the arts it MA for everyone), that always looks good. I managed to fit in literature, languages, maths and science as my qualifying subjects before specialising.
I have to agree, from my experience, the plus sides of an American degree is the breadth of courses can take. I love that part. However I went Ivy league and was a year, sometimes two, ahead in my level for classes. So I ended up taking Junior year and even one Senior year (woah) classes, when I was actually a Sophomore from Edinburgh.
That said, I don't think anyone looks down on US degrees at all.