C.B.
If she's still hitting, I'd say what you are doing is not effective. But you have to remember that at this age, she has a very short attention span and unless something is truly "shocking" to her, she won't remember. With that said, I think she needs a spanking. She needs to experience what she's doing to others. I know that this won't go over well, but I bet you it will be more effective much quicker than anything else you're doing.
Another example that children who are not spanked hit and that spanking does not necessarily teach hitting. Hitting is something that comes naturally to all people and it is only from learning self-control that people refrain from hitting.