The personification in this paragraph is trying to tell you that the waves are crashing harshly and trying to pull the girl into the water. When it says, "It churned and roiled and roared with bubbles and foam." Its acting as if it was an animal instead of the ocean and when it says, "It beat at her, pushing her and pulling her like a cat playing with the mouse it was about to eat." In reality we know that is false however, since this is personification, it's trying to tell us that she was going to become eaten by the wave itself.