Am I the only one who did not know this?
I guess so, because according to Highsmith's Wikipedia entry (and we all know that Wikipedia is never wrong):
Living in New York City and Mexico between 1942 and 1948, she wrote for comic book publishers, turning out two stories a day for $55-a-week paychecks. With Nedor/Standard/Pines (1942-43), she wrote Sgt. Bill King stories and contributed to Black Terror. For Real Fact, Real Heroes and True Comics, she wrote comic book profiles of Einstein, Galileo, Barney Ross, Edward Rickenbacker, Oliver Cromwell, Sir Isaac Newton, David Livingstone and others. In 1943-45 she wrote for Fawcett Publications, scripting for such Fawcett Comics characters as the Golden Arrow, Spy Smasher, Captain Midnight, Crisco and Jasper. She wrote for Western Comics in 1945-47.
So this seems to have been more than just a brief fling.
That information on the non-fiction narratives of famous people sounds very specific, so I'm assuming that I could track them down if I wanted to. But do we know exactly which issues of fictional superhero adventures she wrote? Those sound far more intriguing.
I can't find this information online (well, maybe I could, but I'm not having much luck), so if anyone can point me in the right direction, please pipe up!