Dear Tessrose: If it has been three years since she has had a bone scan and she is having new pain, it is reasonable to do a bone scan. Especially since she has metastatic disease already.
with metastases in liver and lung, the goals at this point are symptom control, managing quality of life issues; anti-tumor therapies may still be useful if they can be shown to be holding the tumors in check to some degree. So as to hip pain: if it's controlled adequately by whatever means it's not relevant to the overall picture what a bone scan would look like. If pain were not being controlled, and if radiation to the area would be a consideration for pain management if it were found to be due to cancer, then a bone scan might be a consideration.