I am so sorry to hear about your friend's mom.
Her prognosis is variable depending on what type of bone cancer she actually has. More than likely, given her history, she does not actually have bone cancer. Rather she has breast cancer that has metastasized to her bones. Either way, it's a long road.
If she does in fact have bone cancer, prognosis would depend on where it is, how extensive it is and whether or not it is resectable (read - amputation). Also whether it is an aggressive type or non aggressive type.
If she has breast cancer that has metastasized to her bones, she quite possibly has other mets also. Lung and brain would be the most likely "other" places. If this is the case then she is dealing with an aggressive disease. Depending on her age and her general health, I would advise seeking out a large medical center and seeing about getting her into a clinical trial of some sort.
You can also check out the nih/nci web site for ongoing clinical trials. I think it's www.nih.gov,
but I may be wrong. You should be able to find it on a search engine pretty easily.
Breast cancer is either relatively curable or a terrible disease, generally speaking. If she's having a recurrence, she's dealing with a tough disease. There are a lot of good existing protocols out there, but if it were my mom, I would get her into a study. We just don't know enough yet to get really good results with the protocols we have.
Good luck! Your friend and her mom will be in my prayers.