I'm an FI and examiner. Agree with Genghis on this. From what the OP describes this student needs to go back to the beginning.
Not understanding the need or having a feel for trimming is always a warning sign for me - it demonstrates a deep lack of feeling for flight and the way the aircraft works.
As an instructor you have to part company with a student who you know is not cut out for flying. And you have to be very blunt with them about why you are doing so. Don't be nice and try to cover up what you see as the problem (but of course keep it polite and professional). You do not want at some time in the future to realise that you taught someone how to kill themselves.
(I remember PERT diagrams! I recall having a plastic template to help draw the different shaped boxes - before the days of computers).