
This book is an authoritative guide to international graphic symbols.
Some of the symbolism they use for computer operations are fascinating
We see a similar thing in games like DwarfFortress where the designer doesn't have access to dwarf/goblin/dragon/water/grass/etc sprites and so has to decide upon a stand-in.
I can't find anything pointing directly to her using heraldic patterning, but it seems her primary reference was Henry Dreyfuss’s Symbol Sourcebook (1972) [limitted preview on archive.org, full available for sale and elsewhere].
And while the book does not specifically feature heraldry or the hatching specifically, several of the examples in the text do contain very similar dot and line patterns as fill in various shapes. Pages 50/1 feature several iconic patterns to indicate earth, rock, natural rubble, rubble, cast stone, marble, slate, brick, common brick, face brick, fire brick, glass, grass, various woods etc in arhcitectural drawings.
There's a surprising durability and universality to certain symbolism. A stick person engraved in the pyramid is reckognized today. Hatching and cross hatching have been used to indicate shadows for hundreds or perhaps thousands of years.
If I had to guess, I'd guess Henry Dreyfuss's Symbol Sourcebook. It was published in 1972, and it seems plausibly the sort of book someone like Susan Kate might have had to hand in the early '80s. https://www.societyofsigns.com/projects/symbol-sourcebook
You can view most of the exhibit online: https://collection.cooperhewitt.org/exhibitions/2318807647/
Worth taking a look!
http://www.amazon.com/Symbol-Sourcebook-Authoritative-Intern...