I have a DD doing GCSEs at Kendrick. She's been really happy at the school, she's made friends and taken the opportunities to engage in extra curricular activities. Generally she's happy with the work and the pace that they go at.
I guess statistically it is "hideously difficult" to get in - our approach was "well it's there, might as well give it a go". I believe it's around 800 who sit the test at Kendrick these days, with another few hundred who sit the Slough test and share their results with Kendrick for consideration. So over a 1000 in total for the last few years, for 96 places.
But please make sure you are in catchment to begin with - no one outside of catchment has got a place since the catchment area was introduced. There's absolutely no point. No appeals have been won either AFAIK in the last 6 years at least.
Although my DD is fairly academic, she's not genius level IMHO. She has her strengths and weaknesses, which she tries to accept - she's stronger in some subjects than other, and that's all there is. It's the same for every Kendrick girl, and in fact every person at every school, surely? So there'll always be someone at the "bottom" but they might be top in another subject.
I've heard my DD talk about people who are amazing at some subject, about people who are slow at other subjects. There is still going to be a mix and range of abilities. The 11+ test is really crude as a selection tool.
The teaching is generally very good, most of the teachers are very enthusiastic and seem to put a lot into the school and the girls. Obviously there's the odd one here or there that seem less good.
Once you start, there's a huge emphasis on school engagement and extra curricular activities. I think the school is well aware that some parents and girls think schooling is just for exams and the pursuit of A*s (or 9s now) but the school's message is to relax and ease that pressure by doing other things for fun.
My DD has done a fair amount of extra curricular sports and music she's really enjoyed that social aspect of school. It would be a shame for the any of the girls to not join in with something, there's a wide range of clubs/activities.
OP if your daughter is not enthusiastic about any school at this stage, then are you keen for her to sit the 11+? Is she willing to do the preparation for the test? Is she happy with seeing her tutor already?
Sorry for the long post, hope it's of some help for you OP.