How to design [Villainess]:
1) Permanent > : D facial expression
2) Opulent, but not revealing outfit, preferably with a long skirt or cape, to give some superficial resemblance to the image of a witch
3) Simple-minded, but social and outgoing personality
No need for any character development of any kind, the idea is that the other people in the story must learn to be humble/social/loyal/hardworking/...
She herself as a person is already perfect, the other people just don't acknowledge because [Villainess] "title".