My Wife Had Grave's Disease And Was Treated With Radionuclide

My wife had Grave's disease and was treated with radionuclide therapy. She became hypothyroid and is receiving replacement therapy. She feels good and well balanced with her current T3/T4 levels but her endocrinologist is worried as she does not have a detectible TSH level. When her T3/T4 levels are decreased in an attempt to increase her TSH from zero she goes through hell with reduced T3/T4. Any thoughts?