Frank, my lumpectomies were pretty easy, as long as I did not move too fast or apply pressure. I slept with my arm propped on a pillow for a while. The SNB pain can be worse. Mine hurt only to move the arm, so just resting was ok. I did get some swelling in the node area, I had a little puffy spot, a small sac, for a while. It resolved, no drains and all is well.
The lymph node area is very tender. Keeping the pain under control is key. She should not try to be a hero, if it hurts, take meds. Of course, call the nurse if she cannot tolerate pain or swelling seems unusual.