What should I do about this mean supervisor at work?

One of the sad realities of life is that we cannot always choose who we'd like to work with. Anyone who has worked for more than a few years will be able to recall difficult or unpleasant individuals that they have worked with. Being able to deal with these people is part of being an adult and the good news is that invariably, the people move on before too long so you don't have to endure them for ever. My advice to you is to have as little to do with this person as possible and on those occasions when you can't avoid her, be professional and courteous. In time she'll either leave or stop being unfair to you.