What are the criteria to decide interval growth?

A 26-year-old lady presents with an incidentally noticed swelling in the right side of the neck region which she noticed about 2 weeks back. She had not noticed the swelling earlier. She is concerned about whether this could be malignant. The size of the swelling is 20 mm × 20 mm. There are no compressive symptoms such as change in voice, swallowing difficulty or difficulty in breathing. She has no history suggestive of hyperthyroidism or hypothyroidism. There is no family history of any thyroid disorder or any thyroid cancer. She has no history of any radiation exposure to the neck in the past. She does not belong to an iodine deficient area. She is getting married in next 2 months but wants to clear any doubts about the swelling. What is the next course of action for her? She is advised to go for thyroid function tests to check for any evidence of hyperthyroidism or hypothyroidism. Her TSH is 2 mIU/L And her T4 is 9 ug/dL T3 is 87 ng/mL Anti-TPO is 42 U/L Should she be subjected to surgery? Should she be asked to go for any further tests?

What are the criteria to decide interval growth?