I don't think a good vet would recommend putting her to sleep unless she was clearly suffering, which it doesn't sound like she is. My dog will be 15 in April, and has the same problem as yours - trouble with back legs and no muscle tone. One thing I can suggest is to stop the Rimadyl and start her on Steroids. I had my girl on Deramaxx, which helped her not get worse, but didn't make her any better. The steroids have made a positive difference. She still has trouble, but is somewhat stronger and definitely peppier than before. Normally I wouldn't suggest steroids, but long term effects are not an issue with these very senior dogs. I also give her tramadol 2x day for pain, and she was also put on thyroid medicine when her last bloodwork showed a need.

Good luck with your baby.

Update:
Made a vet appointment for tomorrow. I talked to my husband about it, and he talked me into going.

I wish you the best on whatever you choose, when ever you chose it, good luck to you, you are in my thoughts.

Cushings is a treatable disease. My dog had it the last 8 years of his life. He lived to be 15 yrs 3 mons.

Cushings causes thinning of the skin. Maybe that why the calluses are bleeding. Other signs are flaky skin, frequent thirst and urination, swollen stomach.

The test is not that invasive or terribly expensive. The medicine is expensive. As I've told others in this forum, if you need med's, get them at Costco. It's half the price than most pharmacies.

Providing the calluses haven't become infected "bag balm" works well on dogs elbow calluses.But you need to make the area/areas where the dog lies more padded, as that's where the problem starts and ends with.

I know this discussion is old, but for anyone else looking for this issue, a padded elbow sleeve can help. It can prevent calluses, and keep existing ones from getting worse. https://mydogswag.com/ is the brand I like.