Fact 1: Though the comics focus more on her ecoterrorism activities, Pamela Isley/Poison Ivy is also one of the DC Universe’s leading mad biologists – and a shockingly unethical one to boot, even by the standards of her profession.
Fact 2: In comics, unethical medical experiments don’t give you cancer, they give you gross super powers.
Fact 3: Harley Quinn has no self-preservation instincts whatsoever and will put literally anything in her mouth.
What I’m saying is that there are absolutely times when Harley Quinn has showed up to a fight juiced up on Poison Ivy’s latest experimental whatsit and proceeded to, like, shoot bees at people or something, so the superhero community is… pretty sure she’s metahuman? But nobody can figure out what her actual powers are because they never seem to be the same twice.