Daughter slapping herself. Her to do so?

Every behavior has a precedent and a consequence. She is old enough to understand what are the triggers for this slapping behavior. You can help her figure out taking care of those emotions and urges in different ways. This will require her cooperation. Second, you need to change the consequence of this behavior. It is getting reinforced because she is getting a reward in the form of attention and probably her demands being fulfilled. You can control this even if she is unwilling to cooperate. Tell her that this is not the way you want her to communicate her needs and frustrations to you. Tell her what alternate ways are. And every time she does it, ignore this behavior. Do not give any positive or negative attention. It will be tough in the beginning. You may need to move away from her space till she calms down. Eventually you will see that she will use this behavior less and less. Simultaneously, reward her positive communication. If she talks clearly, calmly and politely, appreciate her. This doesn't mean you have to fulfill all her demands. Simply appreciate her communication method. Say that you like it when she talks like this. Spend more time with her when she is in a good mood. If things dont improve, see a psychiatrist.