Behavior Issues

Well our sweet little angel is going through a stage (I'm hoping it's just a stage) of being naughty. The past few weeks it has gotten worse and last night John and I sat down and talked about it and decided how we are going to go about handling disciplining her. This past week she has started hitting. Saturday her and John were playing in the floor and she hit him in the face..this was the first time she had done this so we weren't sure if she was playing or doing it to be mean. He told her not to hit and she just laughed..a little while later he told her not to do something and she hit him in the face again...this time he popped her because she obviously did this on purpose. Yesterday while we were at my doctors appointment my mom told her not to do something and she hit her in the face (she goes for the face every time)...so my mom popped her and told her not to do that and that made her mad and she did it again...she is a strongwilled little thing. She has also been throwing some major tantrums lately..if she doesn't get what she wants or you tell her not to do something she will throw whatever she has and starts kicking her arms and legs..it's ridiculous. So last night I had already had enough of her behavior and sure enough she starts to throw a fit because she didn't get her way so John popped her and sat her in a chair. This was the first time that we have used time out because we didn't think she would really understand but she totally understood and was not happy at all about the situation. She sat there and cried and cried and she would look at us and try to get down but she would stay when we told her to. It broke my heart to see this even though I know it is what she deserved..but we have vowed to be consistant so we can hopefully turn this behavior around. Any sugestions welcome!!