is not old for a Lab. My 1/2 Lab was going strong at 10 yrs before she got blindsided by Lymphoma. If she had avoided cancer I'm convinced she would have survived to 15 at least. So 8 years is not an old age for a Lab.

The symptoms and conditions you describe are contradictive. On one hand she has trouble getting up after resting, but once up can run - presumably without limping.

The first question would be: Is the dog at an ideal weight? For a female Lab that's usually around 65 lbs. If she is 80+ as a lot of piggy Labs are then you might have hip problems setting in, and the best cure is dieting and losing the weight. Exercise is better for arthritis or hip problems than losing muscle tone and no exercise. Swimming is the best exercise, and a natural one for a Lab. Pain medications such as Deramaxx may help. This all assumes the dog has weight and hip problems.

If the dog is trim and fit, running well, but having pain when getting up, then you need to get the dog to a Vet for blood work and Xrays to make sure there are no internal problems.