My father is a High Court judge and sits on the pupillage committee at Lincolns Inn. He says:
If you must do a "lighter" GCSE do music, art or a difficult D&T subject.
Good grades in the 2 Englishes, maths, an essay humanity (history or geog), at least 2 of the 3 sciences and a MFL.
Latin weighs very well - particularly with the Old Boys Crowd (who unfortunately are the ones selecting for pupillages at the Inns)
Philosophy and ethics would look good as an AS level
A science, a language and a humanity would be the ideal combination because it shows the candidate has the capacity to think and analyse, communicate a point clearly in a variety of ways and structure an argument.
Interesting but academic subject for a first degree at a good university plus conversion is a good idea. He recommends Birmingham (either Uni of or College of Law) for the conversion incidentally...so possibly avoid UoB for undergrad if she's looking seriously at the conversion there. They like people with a variety of academic backgrounds (ie. 2 different unis) as it shows exposure to different ways of thinking. If she wants to be a barrister then a literary/history/language degree would be a good idea. For a solicitor she should apparently think about the area she would like to go into so to work in the legal side of Mergers and Acquisitions a degree in Economics might be a good bet but if she wants to go to Shell a geology or environmental science degree could be beneficial. Some sectors are apparently quite jargon heavy and Daddy says that as a judge he likes people who clearly understand the complicated documents with lots of jargon and can 'translate' them!
Psychology degrees are apparently frowned upon though, which is interesting because I would have thought they'd be fairly helpful!
Other things that look good on CVs: debating, both the traditional style and things like Model United Nations; involvement in a student paper; involvement in student politics (again strong likelihood of public speaking...); something quirky and interesting to a high level