You explain with discrimination (which was real in the 50s according to most evidence we have) what is in parent's case better explained as a difference in motivation (making a five-figure salary by being responsible for humans is more attractive to the average US woman than being responsible for modules of code is).
Your secretarial school figure is a strawman to make the parent post look like a strawman. There's a legitimate discussion to be had on why women nowadays are found in a higher proportion in medical school and to law school than to CS, and there is a multitude of reasons that are more plausible than purely discrimination. Let's start to tease them apart without merely stopping at the clichés.