@TapiocaSilkpaws
Take the point in doing a mix, although that still means a decision to take 'subjects A&B which I'm not at all fussed about' which seems a bit unsatisfactory somehow. I know maths is quite different at ALevel than gcse, is the same true for Sciences?
I think they should take two they like and one they are good at, rather than two they are good at and one they like.
Motivation is important and if they just take things they are good at but don't like then they won't want to do the work and might do badly anyway. A Levels are a huge leap from GCSE's and if you're not enjoying the studying it will be hard to commit to it.
The one they are good at also shouldn't be one they hate.
I was always an arts person, I took Biology as my Science because I think it is almost the least sciencey science, if that makes sense? It was less technical and more relatable to real life, and I enjoyed it.
(Physics and Chemistry are mostly about about really small or really big things that you can't see, but Biology is mostly about living breathing things)
So yeah, I'd go for two arts, and a maths/science that they don't hate.