I don't know the school; hopefully someone who does will be along soon, however, I know a little about Drama Schools.
Have you and your DD gone along to have a look at the classes on Saturday? Make a list of questions to ask.
It's a bit like asking is a particular university a good one... Yes, some are by reputation, others have amazing departments, and some have other aspects that draw students to them. E.g. sport, campus, area etc. Perhaps considering this Saturday school is similar? Some aspects may be amazing, but others not so. Is it a good fit for your DD? Does it provide what you're looking for?
Ask yourself what you want from it?
Good training for an application to a CDS Drama School later? Or just somewhere your DD can embrace and enjoy a hobby?