Quote 1
"Summon all our people to meet me here as speedily as they can. Call out the giants and the werewolves and the spirits of those trees who are on our side. Call the Ghouls, and the Boggles, the Ogres and the Minotaurs. Call the Cruels, the Hags, the Spectres, and the people of the Toadstools. We will fight." (13.16)
As the head of the forces of Evil, the White Witch isn't playing a lone hand. There are many different types of creatures in Narnia that follow her, and she merely acts as their captain. Evil is not an isolated incident in this world – it's a major dimension of things and wields a great deal of power.
Quote 2
"You have a traitor there, Aslan," said the Witch. Of course everyone present knew that she meant Edmund. But Edmund had got past thinking about himself after all he'd been through and after the talk he'd had that morning. He just went on looking at Aslan. It didn't seem to matter what the Witch said. (13.37)
Edmund's conversation with Aslan dispels all the after-effects of his betrayal. Edmund has begun to change radically and forever, and part of that change is that he's not thinking about himself all the time.
Quote 3
"You know that every traitor belongs to me as my lawful prey and that for every treachery I have a right to a kill." (13.41)
The existence of betrayal in Narnia is what gives the Witch a basis for her power.