It sounds like it could be arthritis. Supplementing her diet with glucosamine and/or chondroiton would certaintly help. As far as cod liver oil goes, it won't help her arthritis, though it would improve her coat. However, I wouldn't go with cod liver oil, as liver is high in Vitamin A and Vitamin A can be toxic if she's given too much. Don't cut down on her exersise -- it can be very beneficial. Just make sure that she isn't doing alot of jumping and make sure she walks on a flat surface rather than uphill/downhill.

I agree with Dragondawg that she certainly is not old for a lab -- she is a senior, but she's still got another 2-4 years on her.

I would take her to the vet and make sure that nothing is wrong internally that may be causing her to hurt when she gets up.

Good luck!