Child slapping themselves

At 14 months, some children do go through a phase of hitting themselves as a way of exploring their bodies or expressing frustration, so it may not be anything serious. That said, since it's happening regularly and you're not sure of the trigger, it would be worth bringing it up with your PD just to rule out anything else. The PD can also watch how she responds and moves during the visit, which gives a clearer picture than guessing on our own. Better to get a professional opinion and have peace of mind than to wait and wonder.