Noon is the hour when she is the most powerful. Several expressions are associated with her. To "step into the platter of the Fair Lady" means to fall under a spell or one can describe a sick child as being "suckled by the Fair Lady."
Water dripping from the eaves forming a puddle constitutes a platter by which the Fair Lady can cast a spell on someone. It is considered dangerous to step into a circle of short grass surrounded by taller grass or no grass at all, since it may be the circle where the Fair Lady dances.