Since all three are good schools in UK, it is down to what are your priorities in education for your daughter and what SHE likes.
Private boarding school does not guarantee a better Uni entry opportunity. So find out if school provides support in students' emotional as well as academic needs. If you can, visit the schools before deciding. Give your daughter an idea what she is in for.
Ask yourself these questions to see what is most important:
1) School / class size
2) Accessibility / Transportation
3) Foreign students: local students ratio?
4) Sports / music / drama facilities?
Here are the schools website and their info page:
CONCORD is in Shrewsbury,3hrs drive from London.
http://www.concordcollegeuk.com/
http://www.isc.co.uk/index.php/40/253
QUEENSWOOD is in Hertfordshire, 40mins drive from London.
http://www.queenswood.org/aboutus/aboutus.php
http://www.isc.co.uk/index.php/40/884
CHELTENHAM is in Gloucestershire, 2.5hrs from London.
http://www.cheltladiescollege.org/welcome/index.asp
http://www.isc.co.uk/index.php/40/207
Reference:
Independent School Council -
http://www.isc.co.uk
Schools Guid -
http://www.goodschoolsguide.co.uk/