I believe that animals have a much different outlook to us. Their instinct is to survive, but if they know that they are no longer fit enough to hunt and feed themselves, they will go and hide themselves away to be on their own. Hard as it may seem, you are helping you cat to do what she want's to do naturally.
We had a cat that got hit by a car years ago. Her back legs were a right mess and we found her dragging herself into the bushes. We took her straight to the vet and there was really only one thing for him to do. 
I know it's early days, but if you are thinking of another rescue cat, I can put you in touch with my wife's step mum. She lives near Brenzett and helps at the Cats Protection somewhere down there. They are always looking out for good homes.
I agree. Animals are driven by that instinct to survive and be healthy, when it happened she had dragged herself and hidden behind the curtain. Sad as it is, we have no qualms about euthanasia being the only option, she has no use of her back legs and cannot toilet herself. She will be discharged to us on Tues (it being a bank holiday) and will be put to sleep in familiar home surroundings. We drove up to Woking to visit her today and she's not the same cat at all.
Dubber, thank you for the rescue suggestion, I appreciate it, it's never to early to get another one. In fact she was one of three rescue cats we got a few years ago after losing previous cats through illness, old age and road accident. However, we still have another 3 rescue cats plus a stray that has partially moved in. That's enough for now
On a more relevant note, the car has been racking up the miles between Kent and Surrey and for the first time ever the long term mpg hit 40. Give it a couple days driving round the congested roads of Canterbury and it'll be back down to 28mpg
