Anyone who would boast of such a wonderful achievement such as graduating from High School three years early would certainly have it available to show you or anyone she would tell that story to.

I think she made that story up and, perhaps some personal or family situation caused her to have to drop out or move to another school, causing her to make up this story.

You didn’t give a lot of information but, was she still around after that where you could see her or, did she simply disappear as if she had moved away?

In a trade school I used to work for, a high school diploma was required for admittance, but we would accept GEDs as well.