How did she graduate from high school?

Gee, I did it by subtraction. I just subtracted the six from the nineteen. :lol:
I can understand your frustration, but there’s more than one problem or question here.
The first is: why should the system require that we identify a person as having gained adequate knowledge of a course in a given field when it’s apparent that s/he has not? As is so often the case, systems decisions are made by politicians (not necessarily legislative, but in this case administrative) who are far more interested in avoiding controversy from the public.
Second, just as some have an almost instinctive ability to play, say, the piano when they are very young and others are never capable no matter how many lessons they take, for some of us our first introduction to the manipulations of large numbers is an immediate joy, while to others (your student) it may be forever outside their reasoning. Of course, another explanation is that she had rotten elementary school teachers.
What we can do about it and what we shall do about it are two different things. We need to subsidize education across the board, from increasing teacher training, paying them more, making sure students can get all the education they want and need at very low cost, etc. Unfortunately, too many of our legislators feel public education is anti-democratic or at least anti-capitalist, so we will probably continue on a downward educational spiral.
Occam