Continuity mistake: When Kate was drawing the trolls in one shot she had a peach coloured crayon, and in the next shot she had a purple crayon.
Continuity mistake: When the trolls attacked Piper outside P3, her bag got flung into the shadows, but in the next shot, her bag was right next to her, and in the light.
Chosen answer: Her agent/manager negotiated a special billing as part of her contract. It distinguishes her from the rest of the cast, probably when she became a producer on the show.
JC Fernandez