Continuity mistake: After Antosis and the Imp Master are vanquished, in a following shot we see Phoebe wearing a robe and sitting on the bed, then we see her "Julie Bennett" reflection in the mirror, but notice that even though the style of the robe is the same, the colorful designs are quite different in the reflection. This happens again later when the sisters and Leo are seen in the mirror's reflection, as they undo the spell to reveal their true selves. (00:33:25)
Continuity mistake: After the opening credits, while Piper tries to persuade Paige to help with the speed dating at P3, in two shots facing the bed and in the shot facing the mirror showing the "Jaime and Jo Bennett" reflection, the lamp on the far side of the bed is turned on. When Leo is holding Chris he walks past the mirror, and in this reflection that lamp on the far side of the bed is turned off, but in the next shot facing the bed that lamp is on again. (00:04:55)
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