Stage 3 with only radiation?  Did she have a radical mastectomy and were there lymph nodes involved?  I was diagnosed with stage 3 and had a radical mastectomy and they removed 22 lymph nodes from my arm pit and 11 of those were cancerous.  I didn't have to have radiation at all.  It was full on chemotherapy for 6 months which lasted almost a year because I developed a blood clot in my left leg so had to deal with that.  I was 33 and that was 15 years ago.  I see you posted this 8 months ago and I'm sorry I wasn't able to answer it then but I did want to answer it now after reading it.  I hope your sister is doing well and that she is on her way to living cancer free (if there is such a thing)  Take care and God bless.