The White Witch is, perhaps, your typical witch. The Witch is evil to the core, without even a hint of goodness within her, which we can attribute to her not being human. Although the Witch claims she is human, she is actually part giant and part Jinn. The Witch is merciless, cruel, power-hungry, and sadistic. The Witch claims the throne of Narnia by brute force. She enchants the land so it is always winter and never Christmas and so that the poor Narnians have no hope. The Witch sways many Narnians to her side out of fear or lust for power, so that the Narnians are divided and are completely terrified. The Witch carries a golden wand that she uses to turn living things into stone—she does this rather frequently when she is annoyed. The Witch is hated and feared throughout the land, but no one except Aslan has the power to stop her.
Allegorically, the White Witch could be a symbol of Satan. In the novel, the Witch plays the role of the "Emperor's hangman" and she has the right to kill any Narnian caught in an act of treachery. The Witch's role is parallel to the role of Satan, to whom the souls of damned sinners are forfeited. The Witch's right to kill sinners is a literal representation of Satan's capacity to impose spiritual death after the death of the body. The novel, however, does not seem to make a one-to-one correspondence between the Witch and Satan. Lewis respected traditional gender roles as defined by religion and probably would not have conceived a female devil. Lewis was also more than a little bit sexist, so he may have done so after all. The Witch is an evil figure, but she lacks the fire- and-brimstone aura that surrounds the Christian image of Satan. Lewis does not follow traditional religious depictions of the characters he uses in his allegories, as Jesus is not generally conceived of as a lion either. The events in Aslan's life, his attitudes, and manners directly correspond to those of Jesus. The Witch seems more generic. It is more likely that the Witch is simply an evil person in the service of Satan, rather than an allegorical representation of the Prince of Darkness himself.