This is just....heartbreaking
. I feel so bad for what this little girl has been through. She is safe with you now.
I'm guessing her health will be a long road ahead of her, but mistreated dogs really can and do bounce back. I wonder if the vet would think it helpful to give her a B12 shot, or a steroid shot, just to boost her up a little.
What about having her lay on a heating pad, on your lap, to loosen up her legs a little? Would that help any? If her legs are indeed atrophied, it will take a while to rebuild muscle tissue. Also, her tendons etc could be very tight due to loss of mobility. Down the road, water therapy may help her.
As far as food....go slow until you get to know her tummy. Does she like peanut butter? If fats are okay for her, then give her a few treats of peanut butter a couple/few times a day...have her lick it off your finger...it's a good little bonding thing too
. Also, try sprinkling Parmesan cheese on her dog food....Parm is nice and pungent and can increase their interest in food.
Once she stabilizes, you may be able to try giving her some food supplementation if the vet is okay with it (like, Puppy Meatballs or something).
Do you know yet if she is pregnant? If she is not far along...maybe spaying her now would be best for her?
Please keep us posted...this is a VERY special little girl.