Predictably, most book covers depict Jirel in a metal bikini or with tin-plated breasts, but this painting properly represents Moore's description of the fiercely independent warrior & strong leader of her people. Some of the sexual politics are iffy now, 70-odd years on, but Jirel is written with her own agency.
Usually classed as Sword & Sorcery, which they are, I think they are closer to Clark Ashton Smith's Weird tales than to Howard's Conan.