Its always going to be a small sample, but the KGS girls she knows seem to love their school, and be really engaged across both academic and non academic elements. It seems to be the only co-ed which has cracked giving girl's sport genuinely equal status.
That said over the years she has met lovely girls from almost all the schools mentioned in this thread and honestly most seem happy, as indeed is DD. Actually I think she would have been perfectly OK almost anywhere which was supportive of dyslexia, but looking back KGS might have been the best fit for her.
(There are so many variables: journey, school food!, teachers, classmates and and and. No one can ever know. The vast majority will be happy with the school they go to, and as long as they meet standards and there are no behavioural issues, schools seem reasonably sympathetic to accepting children who fail to settle in their first school.)
From her feedback the least happy school might be the Lycee, but that is possibly because it is so large, the hours so weird and because the French approach seems to have schools focussed simply on education so not offering the extra-ordinary and priviledged range of non academic activities and clubs available in London private schools. Plus the French system has a lot of subjects and seems to be hard work. So a bit apples and pears.