Hello .....hypothyroidism is due to decreased thyroxin harmone. She should limit their intake of broccoli, Brussels sprouts, cabbage,cauliflower, , turnips... Her TSH level should be under control , don't load her with too much of fruits. Usually woman gains weight during pregnancy, she start loosing weight in puerpurum ... Don't worry .if she is lossing weight drastically you have to consult general physician.