Discipline ideas for a 6 year old?

I'm babysitting a 6 year old girl. She has been misbehaving ever since I got here an hour ago. I asked her parents about discipline and they said its up to you to decide what to do with her. She hits her brother and me, and throw her mac& cheese in the fishbowl. How can I punish her? She also purposely peed on the floor.