Mummy - do you mean would Prospect House prep for PHS or WHS? Yes absolutely! Every year many (most) girls from the middle-top sets are offered places and scholarships at these schools. They are seen as very good schools to get into, but still slightly easier than G&L, SPGS or LU.
So for the most academic handful of girls in the top maths and English set, they might sit say, SPGS, LU or G&L as “stretch” schools; PHS / WHS / KGS as solid options; then somewhere like Ibstock, Kew House, Emmanuel, Surbiton or another School through the Girls Consortium as a safer option.
The good thing about an independent prep is that they will prepare them for ALL options at 11 plus. Different schools have different exam formats obviously, eg some have VR or NVR, some don’t; some use “creative” exercises; some put more emphasis on interview; some exams are largely multi-choice; etc etc. Different exam styles suit different children. The risk with a through-school is that they don’t want to lose their most-academic girls to elsewhere, so they wouldn’t prepare them for other exam formats such as SPGS, G&L etc.
OP, it’s always a bit of a leap of faith with schools but, if it helps, Merlin, PHS etc are all great schools. As I’m sure Squirrels is. You can’t go wrong with any of them. They will all help a child to reach their potential.
I guess their are pros and cons to both routes - if you can get them in somewhere at 7+, then you avoid the 11 plus. But it is a very full-on route, because they are learning to write timed short-stories and doing formatted comprehensions from the start of year 1, rather than just being able to enjoy creative writing and books for the love of it, if you see what I mean? It’s actually very little time to find out what your child’s potential is, because the exams are early in Year 2. It’s called 7+, but most will be 6 at the time of the exams.
Having said that, if they don’t get into the hallowed SPJS or KCS at 7+, it’s not the end of the world because they can always move elsewhere and try again later (or not)!
11+ is more competitive than 7+, but obviously there are more options at 11+.