I don't know anything about the subjects, but I can perhaps help untangle the many level 3 qualifications Pearson offer!
There are actually 5 level 3 BTEC qualifications!
Certificate- between an AS and a-level, depending on grade.
Extended Certificate- Equivalent to 1 A-level (I.E D is worth the same number of UCAS points as an A).
Foundation Diploma- worth about 1.5 A-levels in terms of UCAS points (depending on grade).
Diploma- Worth 2 A-levels. (DD is worth AA)
Extended Diploma- Worth 3 A-levels. (DDD is worth AAA).
In terms of funding, a full time student needs to have the same number of teaching hours as a student taking 3 A-levels. This could be through various combinations of courses but a diploma on its own wouldn't count as full time, and this wouldn't be financially viable for most colleges.
Extended Diplomas are a lot of work- and independent research is certainly required for distinctions in my subject. If she doesn't like to read, I actually think she could get farther with A-levels, where you can just cram for the exam.
BTEC is great for students who are organised and hardworking and like to chip away at something. It's also great for portfolio building and building practical skills.
It can be an absolute disaster for students who can't meet a deadline, or aren't willing/able to sustain work over a long period of time.
I think the best sort of student for a BTEC is the sort of student who struggles to recall things in exams, but tries really, really hard. In exams, often they will only come out with a C/D, but with coursework, because they can research things and use notes to write things up, they are much more likely to get distinctions. In my subject, two of the exams are skills based as well, so less recall is needed.
They can also be good for students who would be U/E borderline at A-level to get something out of the course.