Low normal is actually low for a golden. I would ask your vet to put her in the thyroid meds to see if they will help her. Here are two websites tied to each other that might answer some of your questions and to show your vet. Dr Jean Dodds is a leading authority on thyroid issues. The results can be sent to her to read and give her opinion on what meds she needs to be on.
http://www.itsfortheanimals.com/index.html
http://www.itsfortheanimals.com/HEMOPET.HTM
http://www.itsfortheanimals.com/index.html
http://www.itsfortheanimals.com/HEMOPET.HTM