It's hard to tell from photos, hands on is much better especially in a hairy dog. But, besides a lack of muscle in a dog that runs 6 hours a day, it appears that the muscles are uneven comparing inner thigh to outer thigh. Feel down the back of the back leg and find the bone, the femur. Then feel to the inside and outside of her femur for the muscles. They should be equal in size. You'll need to actually lightly grab the muscle from the rear. None of this should be harsh and if something, anything, you do causes her pain- STOP!
Now run your hand down the back of her leg to the hock joint. Push forward at the joint, one leg at a time. How much pressure will it take before the joint moves forward. Allow her to move forward if she wants to and stop pushing if she does. If it takes a lot of pressure and the joint isn't moving, stop. Does it take the same amount of pressure on both legs to move the joint?
And now love her up. Time for belly rubs.