Characteristics of a Villian?

Villains usually have a disgruntled look about them.

For your stepmother, I would give really highly arched eyebrows, longer eyes (Instead of the more rounded-type ones you see on characters like ariel or snow-white), A long face (So maybe a defined or long chin), defined cheek-bones, high collars, long dresses, high heels, and dramatic make-up. A tall, towering figure is always good too. They never quite have the perfect body shape.

For her hair, you want something that will contrast with the protagonist's. So if the cinderella character has short, curly, wild hair, then you may want to make the step mother's long and straight. And I would try to avoid giving the bad one bangs. They never quite seem to be really evil enough. A bared forehead is a good thing for a villain.

Amy Winehouse beehive!

Exactly what the first person said. You might want to try a tight high bun with no fly-aways so it shows she is strict.