One data point here. D went from 27 October of junior year to 31 June of junior year, so a 4 point jump is definitely feasible. D started taking practice section tests end of February. I think she took the entire test in a single practice sitting once - the baseline test. I gave her at most one section a day. We started with untimed section tests; once the scores went up (over 30) I timed the practice tests.
I made D study the math section again two weeks before the exam. Her score went down from her practice tests. I suspect if I just let things alone, she would have done better.
@novafan1225’s sister has higher grades than D, so I think the potential is there.