Hi '
sorry to hear your girlfriend is suffering with this, and isn't she lucky to have such a caring boyfriend.
Firstly a few questions is she being treated for this ie Medication.And has she been given a diagnosis for the hyperthyroidism ie Graves disease, Hashimoto's, thyroididtis. The diagnosis will determin the treatment.
She will need to have Blood tests for antibodies to determine what is causing the over activiity.....
I myself suffer with Graves disease , the most common cause of hyperthyroidsm, it is an autoimmune problem, my own immune system is attacking my thyroid.
I will answer your questions as best i can,but diet can vary greatly from individual to individual, but there are some basic rules.
If overactive hyperthyroid,avoid any excess iodine which is in many goitrogenous foods, Just type it in and you should get a list including things like green leafy veg such as cabbage,seaweed(v high in iodine),salt, avoid soya milk.
Honey should be ok, as it's natural, but i should avoid, artifcial sweeteners and complex sugars.I have heard a lot of people get on ok with steevia.
alcohol i am afraid and caffeine should be avoided or at least cut down on, carbonated drinks also not good.
I also avoid some over the counter medications, like aspirin, and anything with aspartic acid in.NSAIDs ie nurofen , ibuprofen, and cold remedies.Generally only using paracetamol with a general cold.
Sleeping was a big problem for me when unmedicated,my mind raced all night i could literally hear my heart thumping in my ears.
Your girlfriend should improve once the medication kicks in ,she may .be prescribed a beta blocker to calm her heart down. If that is a problem for her the beta blocker will help, and once her anti thyroid meds have kicked in she can come off the beta blocker.
Personally cheese for me produces way to much mucous and this does not help me sleep, dairy on the whole for me is not good. So if she is suffering with insomnia maybe best to avoid for a while at least.
Please tell your girlfriend to join a thyroid disease forum, she will gain so much insight and on these forums are lists of foods to avoid etc.
Hope she is feeling better soon, best wishes