she can probably remember that its ok for a person to be on her back, but the finer points such as leg aids will have to be taught again. i think its fair for her to have forgotten them after all that time
rugs-if she's doing ok there is no reason why you have to rug her.
muscles-will take a while to build up-be patient
as much hay as she wants is a good basis for her diet, as she digests the hay, the process will actually keep her warm
good quality hay will give her more calories to keep her fat on
grain is not always teh answer to putting weight on- my lad was taken off all grain and actually got fat for the first time ever, digesting grain is hard work and can take more calories than given by the food- ask KarinUS and Peace I think-they've had teh same happen to them
eta have a look here for some more info