If she's abroad for Y11 that might be tricky as she'd need to be in the UK for auditions in the Autumn/Spring term.
BRIT is probably the main one that is free, but a lot of the kids I know who are aiming at Drama Colleges post-18 do a L3 Extended BTEC from 16-18 - more if they are aiming at MT perhaps.
Have a read of the Drama applications thread on Mumsnet. Straight acting is unbelievably competitive and it's not unusual to need multiple years of applications to get a place and a lot of colleges don't tend to take 18 year olds (RADA for example).
The top schools only take around 24 students a year for acting and have easily 2k+ applications for those.
If finances are an issue, be aware that not all colleges are covered by student finance and need big top ups.
Otherwise, if she's more A level focused, universities like Exeter have a very good reputation for drama but it's very different from a drama college if that makes sense. The most important thing is that there is a decent agent showcase - a lot will have pages of alumni and you can click on their Spotlight links and see who they have secured for rep. It's slightly terrifying when some colleges, less than half their graduates have an agent, let alone a high ranked one.
Whatever she chooses, she will also need a very solid Plan B both for post-18 and for post degree as it's the most hideous industry in terms of any kind of work guarantee.
(Parent of child who has been in the industry for 12 years, and who is going down an adjacent route for all those Plan B reasons (already has credits and top tier agent and will maintain training on the side))