The Thorn, unlike many of the super-villains of late 1940s DC, was not revived in the Silver Age, but had to wait until the Bronze Age. Even then, she was revived not so much to give her time in the super-villain spotlight, but to retcon her as the mother of two new superheroes.
Created by writer Robert Kanigher and artist Joe Kubert in FLASH COMICS #89, the Thorn is distinguished for being one of the few "Jekyll-Hyde" villains during this period. In her first appearance, the green-clad villainess showed up to challenge the Flash on his own turf. Thorn carried a small arsenal of thorns that could explode or prick flesh, and she apparently made use of the latter whenever she whirled in place like a dervish, making it impossible for the Flash to lay hands on her. No sooner does the Thorn escape the hero than he meets a woman named Rose, who claims to be the villainess' beneficent blonde sister, hunting Thorn in order to forestall her evil career. Rose relates to Flash a complicated tale as to how she and her sister came to have opposing natures, thanks to the assignments given them by their botanical mentor Dr. Hollis.
Though the story telegraphs the expectation that the two entities are one, even before the Big Reveal, but I find it fascinating that Rose's phony stoty situates Hollis as a rather arbitrary father-figure who allots a pleasant task to one sister, and a grueling, unpleasant one to the other-- though significantly, the evil version of Rose says that she doesn't "mind the hurt." Presumably the second and last Golden Age story-- which I have not read-- reveals the real sequence of events, but the phantom of an arbitrary father-figure is significant nonetheless.
The entire first story appears here on Pappy's Golden Age Blogzine. In 1970, Robert Kanigher would recycle two aspects of this villain-- her schizophrenic double identity and her weaponized thorns-- into his heroic "Thorn" character, Rose Forrest.