Welcome to Health care magic.
1.The survival after
breast cancer in advanced stages - on and average 5 years, some may be more and some less.
2.The survival depends upon the individual immunity status and how it fight with the diseases.
3.In this case your sister seems to be in stage 4 with
liver and
bone metastasis the survival can be any where up to 5 years.
4.Depends on how is the patients food and fluids intake, mobility - once it decreases the immunity level decreases and patient starts deteriorate.
5.I would suggest close people like you should give mental strength to her and end her life happily.
6.And help her with good palliative treatment with good pain killers if required.
No one can exactly say the time, more over with out seeing the patient.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.