What kind of feel are you looking for apart from the academics? Roedean for a example has quite a number of Asian girls and its right by the sea in an urban location. You then have Cheltenham girls which is in a city and the intake is mixed, some overseas and then some local girls. Because it is in a city centre location, the girls are more street savvy. Also do you have any preference for single or mixed sex?
On the other end you have Benenden, more of a country(rural) boarding, in the middle of nowhere and most of the students tend to be from the counties or British expats abroad with a handful of overseas girls.
So in brief do you want the school to be in an urban area, country (ie rural) location? If that doesn't matter how about the feel. Do you prefer a school that has a good number of overseas girls or do you prefer ones with more local girls? Most of the rural schools tends to have more local or rather counties student population as overseas normally prefer urban locations.
Most schools cater for airport pick and drop offs so that shouldn't be a big problem to fly out when they need to.
Exists are nearly every other three weeks and plenty of mid term breaks too. For September 2014, some of the popular schools will have closed their lists but always worth emailing them to see if you can have your name down. There will be plenty of other good schools too. I am down in the South, so tend to know a wee bit about boarding schools down here.
For mixed schools you have Sevenoaks (very academic and very international in outlook), Kings Canterbury etc.
The best thing once you have a shortlist is to visit the schools. You will be surprised something that feel good and ticks every box doesn't feel that way when you visit. Since you'll be far away you want to make sure your daughter is in place you'll be happy with and where issues will be dealt with when they do prop up.
Even though you need to exercise caution reading as some of it is tick boxing but they give a bit of an overview, Ofsted reports are a good start because all boarding schools should have them. Some may be a couple of years old. If you just google name of school + ofsted report, they should come up. You can also go on the Independent School Inspector for more reports here www.isi.net/home/
There is also the Good Schools Guide. this isn't official and tends to be more on the comical side look at these schools. By the time you are done you will either be more overwhelmed or you may just scramble a shortlist. Good Luck.