I am sorry to hear about your mom's setback. As you can see, many people have multiple regimens of chemo. One good thing is that your mom had such good reults on her first regimen. If I had to do chemo again, I would ask about using a combo that included avastin and a platinum based drug such as carboplatin. Your mom and you have my best wishes for another good result with her new treatment plan.
Just to elaborate on a little bit what Bunny said, once the cancer gets into the nodes, it has access to the lymphatic system and can go anywhere in the body. "The horse would be out of the barn" is what my surgeon told me.
Don M