Speaking as a mother of an ex Roedean pupil, Id say you must go and look at the school before you write it off. DD used to be a St Mary's Hall pupil and when the school merged with Roedeanm we were very apprehensive, We needn't had worried as Roedean is a remarkable school which I would highly recommend.
DD was a day pupil and she felt extremely comfortable with the larger percentage of boarding girls. Yes there was a bigger percentage of overseas pupils to UK based pupils, and I wonder if this was/is putting off UK based parents/DD? It's likely to be a vicious cycle which is a shame. DD was blissfully happy there, the support she received was outstanding, the music department was brilliant and the pastoral care was excellent. DD has travelled all over the world visiting her international Roedean friends, so there's a bonus with having so many overseas based girls!
The boarding facilities were good but I'm glad to hear they're being improved. The school sold off the St Mary's Hall building a few years ago and more recently sold what was the SMH junior school building to Bighton College. Roedean never felt cash strapped when DD was there, however, if you want to check on the school's finances, go to the charities commision website and you can read more there.
The only reason we didn't consider Roedean in the first place was because of its reputation of being more superior (we were first time buyers of indie education & a little scared of Roedean); plus the fees were higher than any other school in the area. Not sure how they compare now? I've friends with DDs who either attend or attended The Towers, Moira House, Burgess Hill, Brighton & Hove High, Lancing, Brighton, Hurst & Bedes. DD was highly impressed when she went to a swimming tournament at St Leonard's Mayfield. Cannot vouch for their academics.
You have numerous options to choose from & you need to find the right fit for your daughter. It may be a state school compares favourably to any local private school? if you would like to speak privately please send me a message & I may be able to help further.