Hi
Think Nat (the lady who found the cat originally) from what I can gather, has been the only one to speak with the RSPCA and seems it may have been this same Rehoming Officer who has said NO to everything Nat has suggested.
As a member of the general public, she may have not used 'cat rescue jargon' and therefore hit a brick wall. e.g. board at her vets rather than transfer for private treatment.
So if anyone can get past this Homing Officer to somebody else in authority at the animal hospital, maybe the chief vet, something might be able to be sorted?