RACR, has the RSPCA visited and seen these animals? I suspect not. The local branches have a reputation of being very keen on passing the buck and if they can blackmail you into sorting these cats out, that's less work for them, isn't it? The fact remains - undealt with - that this woman in blatantly refusing to care for her animals or allowing anyone else to without preconditions. What happens when you've cleared out the present cats? Is she going to stock up again?
I have every sympathy for folks who find themselves dealing with situations they can't control or understand. I sorted out 50 feral cats living on a farm last year and the lady caring from them was frantic for any help she could get.
But anyone who fails to put the needs of the cats first and is happy to sit and watch them suffer rather than accept help in any form it comes is guilty of neglect under the Animals Act.
The RSPCA informed Hazel the only way they will will help is by putting them to sleep,
That sounds like a warning that PTS is a possibility if any or the cats are too far gone - and it is a real possibility. But until these cats have been seen by a vet, no one knows their long term chances of survival, do they?
I'd call their HQ and have a chat with the actual Inspector and see if the 2 of you can work together, as bc suggested.