I have had Grave's Disease myself - been about 11 years since I was diagnosed...with that and hyperthyroidism. I was taking meds to try and regulate it, but they did not work for me, so I had to take radio-active iodine pills to "kill" my thyroid. Due to the Graves and hyperthyroidism I was having some eye issues and heart issues as well. They both resolved within months after I had the RAI.
At that point I had to go on synthroid because with no thyroid I had been rendered hypothyroid. That said, my dosage of synthroid does have to be monitored closely as I can and have reverted to hyperthyroidism due to over dosage of the medication. How often does your mother have her levels checked? I think it is most likely that she is taking too much medication and needs to be put on a lower dosage and that will take care of the issues.