I have just added Sophie's blog to my links. I found that she wrote an article together with her parents, and here is what her parents said
When Sophie was five or six years old, we noticed that when explaining something, she appeared at times to be unable to get words out quickly enough -- as though her brain were racing ahead of her ability to say what she wanted. At first, this happened only occasionally but, as the weeks and months went by, we noticed it more frequently. Friends we talked to said it was a common phenomenon at Sophie's age, and probably she would grow out of it.
She didn't; rather, it happened more often, until we came to see that Sophie had developed a "stutter"of some sort. Inevitably, Sophie herself soon became aware that sometimes she couldn't say sentences smoothly, and this frustrated her. However, she talked fluently enough if she didn't think about her speech, and so it seemed to us that the less we drew attention to it, the better.
These statements drive me insane because I have no good explanation why stuttering got more and more frequent. Now, if there is a defect or default, it should just be noticable right away with the same frequency or intensity, or be less because the brain gets used to it. I can think of three possible modes of explanation: some chemical imbalance getting worse over time, a virus infection spreading slowly and then stopping, and some adaptation mechanism that escalates the situation (like you have a little spot on your face, you open it, wound gets infected, bigger spot, and so on).