I am sorry to hear that your beautiful cattle dog has developed such a debilitating condition. Unfortunately bone cancer is aggressive and very painful. Pain relief is therefore usually prescribed for these conditions and in some cases, if the disease is diagnosed early and the patient has healthy joints, amputation of the affected limb is recommended. I would recommend that you speak to your veterinarian about the next step for your dog, they would know from the radiographs how aggressive this cancer is and can also assess the degree of pain she may be suffering and therefore guide to appropriately.
I understand completely from my own experience how difficult it is to decide when the time is right to say goodbye to your best friend. They are lucky in the sense that we are able to given them a dignified end and this is sometimes the kindest and most selfless act of all.
I wish you and your dog the best of luck in this difficult journey.