Any advice on gaining muscle mass in back legs?

[Vinorosso74]

Vinocat who is 14 (approaching 15) spent 16 days in the cattery (came home on Monday) and as DD has put it "lost her spring" in her back legs. Her weight is down to 2.2kg and in the second week her diabetes went a bit haywire-high glucose readings hence the weight loss.
She can jump on the sofa but not the beds and it's quite upsetting to see. Any ideas of anything we can do at home to help regain muscle mass?

I've no idea. But could you give her something to step on to help her to get on the bed?

I know with my dog we were advised to walk him upstairs and hills to strengthen the muscles in his back legs but I'm not sure how you could persuade a cat to keep walking upstairs .

Since I posted she is getting better and can jump on DD's bed now. We did put a box at a mid height to get on ours and she was on the bed during the night but no idea if box was needed or not!
She seems ok with the stairs and went half way up those in the communal hall today! I've let her in the garden albeit supervised so she is happy with that. Seeing vet on Monday so hopefully she'll keep improving.