What breed do is your girl?
Is she a normal weight for her breed?
This may indeed be some arthritis, but there is a possibility that this could also be a problem common to the long bodied and short legged dogs call invertebratal disc disease. This is what is similiar to what we call a herniated disc or slipped disc in humans. This could account for the weakness in the rear end and having problems getting up. An xray would not show this problem, but it would show if it is arthritis. In any case the Vet can give some medication if it is causing pain. As far as helping her you can use a towel and pass it under her stomach to help her get up from a laying down position. You can also use some Glucosamine for dogs that is sold at pet supplies and also a good omega 6 vitamin. This may help if this is arthritis. Joan
I know you love your baby and I wish you much luck in getting her feeling better.Best Wishes! Joan