“My daughter has hyperthyroidism. Is this a "forever" condition?”

Good that her hyperthyroidism diagnosed and she started treatment. Often it's caused by autoimmune problems in this case she would need endocrinologist care for a long time. But just Iodide deficiency could improved in short time.

Hyperthyroidism is mainly an autoimmune disorder where by the body's immune system makes antibodies that continuously stimulate the thyroid gland to make excessive thyroid hormone (thyrotoxicosis or toxic thyroid). This autoimmune disease is called Grace's disease. There are other causes of hyperthyroidism as well. But in children, the most common cause is graves disease. This disease is mostly treated with antithyroid medications. In the USA, we use mainly methimazole and PTU. Of course, radioiodine ablation and surgically removed are other options if appropriate.

When the thyroid is treated with antithyroid medications for about 2 years, about 25%-30% may go into remission when antithyroid medications are discontinued. Therefore, the answer to your question is, in some, hyperthyroidism will have remission. Some will require long-term treatment, and others may require surgical removal or radioiodine ablation. Since medicine is an art, the decision is left to the patient and the physician to determine the best treatment option.
Good luck.

Hyperthyroidism is a chronic disease and treatment is variable. Depending on the cause (most common is Grave's disease) treatment could range from medications, radiation with iodine or surgery. It is important to be treated by an endocrinologist.