D.K.
Possibly a dog Nsaid like rimadyl, deramaxx, previcox and metacam are a few. It will depend on what is actually wrong with the leg, but the meds can make a huge difference. Possible bloodwork before and after starting to make sure she does not have any kidney or liver issues. The meds can turn an older dog into a more playful and active dog. Also if she is overweight at all getting any extra off can help. There are rehab exercises that can help, cavaletties, swimming, exercise ball that is big an oval shape. Your vet probably won't mention all of those, but they are out there. Our dog used to frequently sprained one rear leg and her hip joint is good, but bot great on that side so we have done a littlebof everything over the years. Good luck and hope your vet can give het some relief.
Added: accupunture can work wonders and testing for tick borne diseases can be a good idea if it has not been done or is not done with yearly heartworm testing. Might be a long shot since this is on going, but you never know.