I'm sorry. I don't really have any recent knowledge. What I do know is that Rosebery in Epsom is the only all girls, non-grammar state school in Surrey. When I went there the results were good (about 83% pass rate A-C including Eng, Maths and science at GCSE). Not too sure about now but I can tell you that we lived (parents still do) within a 5 minute walk of the school and we regularly got letters through our door and still do, asking that " if you are considering selling your house in the future then please call us. We have two daughters who we really want to go Rosebery and so want to buy a house in the area". People have moved into our road when their daughters are just starting primary school, with the intention of getting them into the school. So considering that, I am guessing it is still considered a good school. We used to have school discos with Glynn, the all boys school. We also did joint school exchange trips to Germany/France with Ewell Castle school, a private boys school.
Sutton High - I am surprised that it isn't nicer. I have never been to look round it but considering it is private I thought that it would be quite nice.
The school that is probably in highest demand is Nonsuch Girls Grammar in Sutton/Cheam. Children have to set the 11+ to go there so it depends on whether you want your child to do that. From what I have heard though, it is very competitive so even if a child does get a good pass mark that should be good enough and would be for another grammar school, at Nonsuch it may not be just because the school places are in such high demand.
Other girls schools off the top of my head are St Philomenas Catholic. It's in Carshalton but I think is classed as a London school rather than Surrey. Not too sure of the results there.
Greenacre in Banstead is an all girls private school. I knew several people who went there and seemed to like it. I think it is quite small and has good grades.
All of these schools are within the Sutton/Banstead/Epsom area but I also know of several in the Guildford direction as well. Not sure if they would be too far south for you but if you are interested then happy to tell you about them.
Don't ask why I have so much random knowledge about schools. I haven't quite figured that one out myself!!! lol! I have a brain that seems to store lots of knowledge that is of no use for me!!!