Usually cats become hyperthyroid if they develop thyroid problems. We do not have a product directly for that, but your friend could try our homeopathic product called Dia-IonX that was formulated to help with endocrine imbalance. It is easy to give by adding 10 drops to the food for breakfast and supper. It might also be good to try homeopathic Thuja 30C from the health food store. She could give one pellet at bedtime for about 3 weeks.
If things do not improve then her veterinarian will want to prescribe medication. Another consideration is to consult with a veterinary acupuncturist.