Thanks fpr your suggestions re: my friend's continued voice change. She is going to a new endocrinologist who has ordered several tests, including an ultrasound, So she is getting the help she needs. Again,,,Thank you for your posts!
ottom line, your friend needs to see a specialist where they can run tests to see if her vocal cords are damaged, specifically a ENT doc. A Goiter and nodules can surely affect the voice.
Is your friend a smoker? Or was she one? The reason I ask is that I used to smoke and because of that, along with many years of severe acid reflux, I had a lot of excess tissue build up on my vocal cords. My voice got very deep and eventually, I could barely make any sound and it, actually, hurt to try to talk. This was because when I tried to make sound, my vocal cords didn't vibrate like they were supposed to; instead it was the excess tissue that vibrated. I quit smoking, then underwent 2 surgeries to remove the excess tissue. My voice is "normal" for the first time in most of my life.
Nodules and/or goiter (inflammation and enlargement of the thyroid) can impinge on the laryngeal nerve and cause voice changes. These usually manifest as a "gravelly" voice or hoarseness or loss of a singing voice. However, I have not heard of it causing total inability to vocalize.
If she knows she has nodules, she should pursue her thyroid issues. Although it may not be the only cause, it certainly could be contributing. A thyroid ultrasound would reveal many of the physical characteristics of her thyroid and give her a point at which to start.