First of all, I love this post because you are what many of us needed in our own parents as kids. That being said, I think it may be neurological trauma. I also had no familial stuttering and it came suddenly in the third grade, which was too late to be considered genetic. If this is the case, there is no known cure, but my father was diagnosed with a neurological disease that ultimately killed him and I learned a lot about neurological conditions at that time that I now realize is true of my own, even though stuttering won’t kill me: the less stress, the better the sleep, the stronger the love, the better the chances of reversing what they said could not be reversed. I’m the first one to stand up and say anyone advertising a cure is a scam artist, but I have been through periods of fluency in my life and they were times that were filled with great sleep, nutrition, and love. also, I some kids stutter for brief periods as kids and shake it off. Hopefully this is the case for yours. Lead with love.