Hello and welcome to Just Answer.
I am so sorry that you are going through this with your Cheeney. Tough situation for all involved,
Bone cancer is indeed very painful and as you are experiencing the oral meds often can't control the pain. Long acting opiods (extended release oral morphine) can be added instead of the tramadol, but there is still pain involved.
If you don't think that bone biopsy/amputation is an option, you might still consider radiation simply for pain control. With this we usually give three or four dose of radiation to the affected area and this is quite effective for pain control.....but doesn't really prolong life....just help with pain.
I really watch for decreases in appetite to be a good indicator of when the time is right to consider euthanasia. This is not always the case for some "chow hounds", and you have to consider if there are any pressure sores forming on her elbows and hips and how much you can handle helping her get around.
She sounds like a dog with a great spirit. Making the choice for when euthanasia is the right thing is so personal, and honestly, I have had clients that make the choice as soon as the diagnosis is suspected. Others wait until the dog is having trouble breathing (implying metastasis in the lungs). You just have to look at what you consider good quality of life for her and then decide. It is never easy!! I feel for you as I had to make the same choice with my dog several years ago.