Honestly, it's far better that she takes subjects she's good at (and preferably enjoys). When she's the other side of university, very few employers will really care what subjects she did at A-level (unless they're very niche roles). In fact, most don't even seem to care about the subject of the degree these days, except for roles which specifically require in-depth knowledge of a particular subject.
Thing is, unless she's going for an academically-focused role, it's likely that she'd need to have a lot of the things she learned at university trained out of her in her first job anyway - that's certainly true in my world (IT and development) and I've heard it said in a lot of other areas too. Getting the degree itself is the important part, because it shows an ability to get down and work.
Basically, relax. Let her do her thing, and she'll discover where she wants to go with her life - the important part being that it's her life. That, to me, is the most critical part of university; it's where you go to learn how to be independent, and to figure out what you want to do with yourself for the next forty or fifty years. Don't put additional pressure on her to decide that right now, because whatever choice she makes under those conditions...odds are it'll be the wrong one, and she'll resent you for it for a lot longer.