When the apple was ready, the queen painted her face and dressed herself up as a peasant woman, and crossed the seven mountains to the cottage of the seven dwarfs. (Snow White.186)
What's the point of being an evil sorceress if you don't also get to disguise yourself from time to time? Not like it's all that necessary; Snow White lets the evil queen in disguise give her three poisonous things (the apple being the last) over time. Sometimes you don't even have to be all that cunning to off your naively trusting stepchild.