Im asking on behalf of my mother who has an under active thyroid. she takes levothyroxine and she wishes to take multivitamins for her health. i wanted to ask what vitamins are beneficial and which ones are not recommended as iodine is not ideal ?

None unless deficien: Many studies have looked at whether there is overall benefit for people who take multivitamins and those who don't, and the answer is no benefit (but also mostly no harm). The best treatment is a good diet with lots of vegetables and fruits. If someone has a particular disease or condition in which they do not absorb nutrients normally, or eats a very restricted diet, then a multi-vit is useful