Necrosis after breast cancer?

My mother had surgery over 2 years ago to remove a small tumor in her breast. It was deemed stage 1 ductal cancer. It was removed and she went through radiation. She has regular mammograms and takes her cancer drug ( Arimidex) daily. She just had her most recent mammogram and they discovered two small "changes" or nodes in her breast. They couldn't tell from the  mammogram or an ultrasound what they are so she has to go in for a biopsy in two weeks. She is worried beyond belief as you can imagine. One of the nurses said the marks could be necrosis after the surgery and radiation she had. One of the marks is located right near the site of the scar tissue but the other one is much farther away, even further than where the cancer was discovered. I would like to know how common it is develop necrosis 2 years after surgery and/or radiation and what is the likelihood that someone would develop two spots, and that one wouldn't be near the scar? She can't feel the spots as they aren't near the surface. My concern is that she developed two spots and one isn't anywhere near the surgery. I would like to give her some hope before the biopsies as she is a nervous wreck and two weeks is a long time to worry. Please if anybody has any info I would really appreciate it. Thank you.