I'm sure my post is not going to make you feel better.
Back in 1995, a cold nodule was also discovered on my thyroid. It was on the back of the thyroid and the surgeon was not comfortable with a biopsy and feeling like he could get enough samples.
So, I opted for surgery. Like your wife, I had half of the gland removed. They did what is called a "frozen section" pathology while I was still in the OR. It came back benign. I was stitched up and sent home the next day. The following week, I went back to my surgeon for a check up and I got the bad news that the final, full pathology showed that there were some cancerous cells within the nodule. I also had cancerous cells "peppered" in the other parts of the gland. So, I had to go back and have a completion thyroidectomy. Good thing too. While I didn't have any lumps on the other side, I had many, many "micro-cancers" in my gland.
All is well now, but please be prepared for anything. I belong to an on-line thyroid cancer support group and my situation happens often enough. Thyroid biopsies are notoriously inconclusive because the whole nodule will not be cancerous and needle biopsies can miss important cells. The only "definitive" thyroid needle biopsy is a positive one OR to have surgery and have it looked at cell by cell (like they will for your wife).
Good luck and please keep us posted here. If you have any questions, please feel free to PM me.