What is the prognosis for metastatic breast cancer to hip bone?

Treatable,NotCurable. The term "prognosis" is like an on/off switch and does not take into account disease control and quality of life. After all, diabetes is incurable but doesn't have the same connotation as cancer. Many breast ca patients with bony mets respond very well to rx and can live for years with this. It is best to focus on response to rx rather than cure.
Fairly good. Metastatic breast cancer has many good treatment options available. These include a dozen of different chemotherapy drugs and hormonal drugs that can control the disease for several years and thus prolong life meaningfully. If it is one spot on the bone even radiotherapy can be an option of treatment. So just ask all these questions from her oncologist and you will learn and find the answers.