What Is The Life Expectancy Of A Person With Stage-4 Breast And Bone Cancer?

I am trying to help to prepare a friend for her Mothers imminent (I believe) passing. What would the life expectancy be, approximately, with stage 4 breast cancer as well as stage four bone cancer, mestasticized. She starts radiation (full body cast being applied today) tomorrow and I am thinking that realistically, she probably only as 2 or 3 months at best. She is now on Methadone as well as Oxicodone. Thank you so much.