How to deal with a child who continuously is defiant and misbehaving?

My four year old daughter has really been testing my patience the last few days. She has just had a terrible week when it comes to behavior. She is getting into things that I have asked her not to get into, backtalking, and just not listening. She will look at me when I tell her something and tell me "NO". I have been putting her in the corner, but it is just not working. I know there is a good child under there somewhere, but it is certainly not been showing here recently. My husband gave her a at dinner last night, becasue she was misbehaving at the table. I don't a lot, but sometimes it seems the only way to get through to her. I just don't know what to do, any suggestions?