I hate to be blunt here but having someone stop synthroid cold turkey is very bad advice.
When someone is on external hormones, doesnt matter what kind, it forces the bodies own production to stop. If they have been on synth for a log time you cant just stop taking it and expect the thyroid to kick right back in. This isnt a light switch you just turn on.
The fact they were put on synthroid to begin with likely means they had suboptimal thyroid function then atrophy from lack of use....much like a broken arm in a cast.
You really shgould have had them on selenium, Iodine and all cosupps until sufficient and then slowly and gradually over weeks reduce their synth dose.