Hello, this is Dr. David. I have read your question and am ready to help.
i wouldn't do a PET scan
reactive nodes enlarging to fight an infection or reacting to the surgery can light up bright on a PET scan as well
if one of those nodes are really enlarged like greater than 2cm, she should have a lymph node biopsy to be more sure of what is going on in the node.
those nodes very well could all be benign reactive nodes reacting to an infection or inflammation
NHL typically is not in lymph nodes smaller than 2cm
she could have a viral infection
mononucleosis could enlarge many body lymph nodes
that should be tested for.