So My Wife Had Her2 Metastic Stage 3C Breast Cancer

So my wife had her2 metastic stage 3C breast cancer 3 cm 12 nodes positive out of 33 taken out and into chest cavity She underwent 33 chemo tx and I think 33 radiation almost 2 yrs ago now. She is currently experiencing severe chest and back pain in the surgery area making it hard to breath and move. We discovered a large shingle blister behind her armpit yesterday. Is shingles related to possible cancer relapse or is it just shingles?