You need to find a punishment that is punishment. Like maybe taking toys away or something. Then you need to be consistant. Everytime she is rude, has an attitude, or misbehaves, then she needs to be punished. Just calmly tell her she should not do that, what she should be doing, give her a warning, tell her she is being warned, then if she does it again, follow through. Dr. Phil had a show on really bad little girls with attitudes (way worse than yours). He suggested taking ALL toys out of room and putting only their bed in their room, then giving toys back for minding, good behavior, good attitides, etc. Sometimes it is hard to punish as much for the attitude, but you have to. Maybe make a chart about what you expect and dont expect of her, and punishments. So it is her choice and she has the decision to make.
Good luck,
K.