What Causes Severe Nausea And Headache After Taking Synthroid 75 Mg?

Hi My daughter age 28 with Thyroid disease and poly cystic ovarian disease she takes synthroid 75mg. for about 3 months she has had reoccurring nausea and headache to the point that she can not walk and must lay down. They come on at different times morning, afternoon & evening and last for different amount of times. sometimes for a few hours and others for a day. it always starts with feeling nausea first and feeling a little off like not being able to focus. She only gets them randomly about once a week or every other week. At first she thought she was just dehydrated because she had not had a s much water as she usually does. But she now realizes that even when she is faithful with the water she is getting it again. She is not over weight and takes her medicine like clockwork. She has mentioned it to her Dr who said it might be migraine. how do you know and how long should she just be watching it? I am concerned as she has never had headaches in the past. She had an Aneurysmal bone cyst when she was 2 in her growth plate of her elbow and was treated for 10 years with it. It was a tough one for sure which is why she has a very high pain tolerance so for her to not go to work is a big deal .