Camden School for Girls - HELP!

State sector in London has experienced an accelerated deterioration education resources, it is hard to foresee how to reverse the situation in the next few years.

@liopwr also, Camden offer ancient greek and Latin as well. Really good travel opportunities and tons of clubs. OP can you afford the travel opportunities at Queen's on top of fees? If not, than I wouldn't even take that into consideration.
I'd say music is probably better at Camden than at queen's but yes, the resources will be stretched. However, independent schools are stretched too. They're having to balance reasonable fee rises with true cost increase and a lot are swallowing the difference. Recruitment is a problem in both sectors. Obviously it'll be no where near the pressure state schools are under, but the pressure is there.
Sport will definitely be better at Queen's.

Queen's Coll had more of a similar vibe to Camden pre-Frances Ramsay, from the lack of uniform to a liberal grown-up attitude to learning. It's since become more standardised with better exam results and more conventional cohorts, none of which is negative, just different. If you loved QC you may find CSG a tad uncomfortable, especially in a few years' time, when hormonal and academic pressures kick in. As always it depends on what you want and need from a school. CSG will be under heavy resource pressure, while you're providing the resources at QC. Both are competently run, so you get the package you choose.

@liopwr "Although OP's daughter may of course opt to mix mainly with the girls with the Queens-type background."

It's very unusual for anything but this to happen. Sometimes it does, but it's rare.

"your DD will mix with very similar girls to ones at Queens"

Very different cohorts - some parents at CSG will have similar backgrounds and income to those at Queens, but there is some deprived housing in CSG catchment and families on that income won't be paying the £24k fees at Queens (that will be higher than their entire household income in some cases). Although OP's daughter may of course opt to mix mainly with the girls with the Queens-type background.

Extracurricular opportunities at Queens are broader especially for sport - gymnastics, rugby, cross-country, netball, basketball. Used Paddington Rec, Finsbury Park for athletics, Marshall St pool, Frame for fitness classes. Travel opportunities are good - ski trip, music trips, sports tours. Language options are French, Spanish, Italian and Mandarin - at CSG the options are French or Spanish. The clubs offering is richer. At secondary it's easier to fit in extracurricular activities elsewhere if needed, and you can go on trips outside of school but it's convenient to have it on site and good to build friendships within the school. Uni options may be better if going to state, but that has to be balanced with the general under-funding and limitations of state facilities and staffing levels (check noblegiraffe's threads if you're unaware of the crisis in secondary schools right now - CSG isn't immune despite being supported by so many middle-class parents).

I think you just have to visit both and go with your gut instinct. I've known families who are happy at both schools and whichever option you take, the girls will be happy.

I don't know anyone that's unhappy with it but than again the people I know that send their daughters there aren't ones that would admit it was a mistake. It's cramped but overall you'll save a lot of money, your DD will mix with very similar girls to ones at Queens and will likely get the same results. It depends if the queen's fees are a drop in the ocean or not. Be mindful that by the time your DD is in Y9 or 10 you'll be looking at fees of 10k a term.