Hello, welcome to Just Answer. I'm Dr Ralston.
Although I have seen Pitties get as old as 16, I haven't seen many of them get that old. At 15, I would have to agree that we are probably getting close to the end for Diamond.
But, we can help make her comfortable until that time.
There are many options. Some are better than other.
1. aspirin - Aspirin is used in animals to treat pain and arthritis. The dose that is often used is 5-10 mg per pound twice daily. So, a 50 pound dog would get about 250-500mg twice daily. I would always start with the smaller dose.
2. glucosamine and chondroiton sulfate - this can be purchased at any pet store or from your Vet. And, I think it does help too, but mostly early rather than later.
3. There are other medications that you can get from your Vet if the aspirin does not help. Tramadol, Rimadyl
, Gabapentin are a few of the more effective ones.
If the pain is very specific and she will let you, she might benefit from warm baths to help ease the pain.