Queenswood near Potters Bar in Hertfordshire is very sporty! Weekly boarding if you live further away. Tennis is a major sport here (about 22 courts) as is hockey but girls have a wide choice and many excel at a variety of sports.
It depends which sport, and whether you want elite sport or a school that encourages participation. Remember schools which focus on winning can offer very little to the average pupil.
KIngston Grammar is head and shoulders above most schools in several girls sports. Its co-ed, but unlike many co-eds, girls sport is not seen a poor third after rugby/rowing, and other boys sports. Surbiton is not bad, nor are LEH and JAGS. Reeds Cobham? Again co-ed.
If it is elite sport you are looking for, the best starting point is to look at which schools win the various IAPS competitions, or has pupils represent them. sport.iaps.uk/
I am surprised at LIZS suggestions. DD played against at least three of the schools mentioned in a couple of sports and they were pretty weak. Lots of Wycombe girls seem to pass through the school with only a passing nod to sports participation.
The co-eds are strong if your DD enjoys 'co-ed' sports. KGS and Alleyns are particularly good for girls' hockey and cricket. The single sex schools tend to be better at netball + lacrosse as they can employ specialist staff.
Interesting list RosyPosy but it must be very narrowly focussed on certain competitions only - can't account for a boy's school as strong in sport as Dulwich not making it into the top 50 otherwise.
Also in choosing for sports, look at the number of sports on offer, as well as First Team results. How many and which sports do they have qualified coaches on the staff (or retained peris)
And one useful little side angle is how do they select their sports scholars? Are they looking to nab pre-formed excellence (club/county/national) or are they confident enough in their coaching that they select all rounders with bags of potential but perhaps less track record (as at primary age, it's as much about the parents knowing the club system and having DC join good ones, as it is about the pupil's interest/aptitude/fitness).
I think newt, that is partly based on variety of sports as well as success in those, so schools like Dulwich which have superb rugby teams may be disadvantaged if they don’t do lots of other sports to a high level as well. (No idea if Dulwich are good at any other sports or not)
Kingston Grammar has impressive levels of participation in sport. Something like 93% represented the school in a sports team last year iirc. Pretty impressive.
To me that says a school is strong in sport. it's very easy to have a 1st team with lots of superstars (offer big sports scholarships and manage their academics) but not so easy to have high levels of participation throughout the school.