The worst punishments are the ones that aren't sexual, but are something you dislike alot.

Like ironing. I had a dom make me iron all of his shirts one night. I HATE ironing. Writing is also a good tool. Writing I will not X 500 times is enough to change any one's mind about behaving badly. Standing in the corner for 20 minutes is also something that's enough to drive me batty. Be creative with your punishments. If she dislikes it, It'll usually make a great punishment!