Hi Antonio,
Firstly, I would recommend she saves up as much money as possible before she comes here. The U.K. is not the cheapest of places.
The University of Cambridge
(
www.cambridge-efl.org ) do LOADS of different kinds of English courses - their site is VERY informative and well worth checking out.
You can do their courses all over the country, including most of the places you have mentioned.
The following book might be useful:
The EFL Directory - The Complete Guide To Learning English in Britain
ISBN: 1 84024 205 1 (Code number)
Price: about 15 euros.
I can't actually recommend it as I have never read it, but perhaps you could find a copy in a bookshop and look through it!
You didn't mention London - International House
(
www.ihlondon.com ) do excellent English courses that include accomodation if required - no shortage of things to do either and good chance of part-time work. Depends if she has the money to pay for the fees.
Bath, Bournemouth, Brighton, and Oxford are all nice places - I know absolutely nothing about Canterbury except that it has a cathedral - they are all large enough to find plenty of things to do after studying is over, (good nightlife, easy access to pretty countryside, lots of student activities...), and also large enough to provide part-time work.
She will, however, be competing with lots of other students looking for part-time employment. I think Bath is GREAT - it's very pretty and the surrounding countryside is wonderful.
Bristol is also a good place to consider, as is Cambridge.
University residence can be tricky unless you are actually doing a course with the university - however the college she enrols at may well help her find somewhere to live.
Flat sharing is relatively easy - good places to look are local papers, student noticeboards. Prices can start as low as £25 a week for a room in a shared flat or house - it really depends on where she is and which part of the city/town she ends up in.
She might find a family who want to learn Spanish which would be a good cheap way of living here - best to do that via an agency(?), not really sure.
Working in a law firm might be tricky as it depends on how long she will be here for - possible secretarial work in a solicitors office, she'll just have to check the local papers, or even turn up at a few offices waving her degree.
You say that "the accent is better in the south"........well.....I wouldn't dare to comment on that! I'm from London and have been accused of having a "BBC" accent which many people consider dull and boring. If she should end up studying in Leeds or Manchester (both "north"), it is unlikely she will end up with a strong northern accent - unless she plans on living there for a few years.
I think the Cambridge site is your best bet to start off with.
And as for Norwich.....well, I wouldn't want to live there, but then there are LOADS of places I wouldn't want to live in - that's why I'm trying to work in Spain!
Good luck - if she makes it tell her to drop me an email and let me know how she's getting on.
PS I hope to come to Madrid to do a teaching course in October - I may well be contacting you about a few days accomodation in September! You've been warned!