The image of the dangerous crone is a very old one. The brothers Grimm used it, and they weren't the first by far. In addition to the ugly, old hag, there's also the beautiful and dangerous enchantress like Circe from Homer's Odyssey, or the older earthmother type. Witches in literature - and in comic books - are sometimes depicted as satanic and evil, sometimes druidic and nature-loving, but always powerful.
Triple Goddess Style
Modern practitioners of witchcraft often use the imagery of the triple goddess, which mirrors the three stages of a woman's life and the phases of the moon: Maiden (youth, innocence, power waxing), Mother (motherhood, fertility, power at full), and Crone (age, experience, power waning - sometimes). These concepts are mirrored both artistically and in literature with the beautiful and young nymphette, who's innocence is both naïveté and literal; the lush mother, full-figured, older but still attractive, she's lost her innocence, but isn't cynical; and the aged crone, who's body may be frail, face may be lined, but her experience and sometimes cynicism make her a powerful force to be reckoned with in spite of her frailty.
Brides of Satan
The idea that witches were tied to Satan is hardly a new one. The men and women who died (none were burned in North America, that was the Europeans) at Salem town were accused of being in league with the devil. Anton Lavey with his founding of the Church of Satan in 1966 helped bring this concept of Satan's brides into a modern setting in the eyes of the fearful.
While Lavey was turning Christianity on its head (literally), others were embracing the idea of the feminine divine. Neopaganism, inspired by Margaret Murray's 1921 book The Witch-Cult in Western Europe, started becoming open and public in the 1950s and '60s. These modern pagans use history and mythology to construct what they believe is the Old Religion, that predates Christianity. (In fact, there are no written records of historical witch-cults beyond Murray's theories, which many contemporary historians have disputed.)