I have a character who is mute, and I've been putting off on exactly why she's mute. Basically what I've been going with is that she is unable to make sounds that require the use of her vocal chords. She can whistle but not hum, cough but not laugh, so forth. I thought perhaps having her have selective mutism, but research shows most selective mutes also have shyness and social problems and are know to talk at some point when they are comfortable, which doesn't fit this character. I looked into paralysis of the vocal chords, but that comes with a slew of breathing/eating/drinking problems. Other vocal problems I found cause only harshness, not full, life long mutism.
So, my question is if there's anything that can stop her vocal chords from emitting sound but not cause other problems, and can last her entire life?