Continuity mistake: After Prue and Phoebe send contagious Piper back up to bed, it cuts to three consecutive shots of buses arriving at camp. In the first shot, the bus license plate is white with the number "2IAB345" and we see markings on the bus as the counselor exits. The second closer shot shows two kids exiting the bus. Then in the third wideshot, with those same two kids beside the door, the license plate is now blue with the number "876QPD" and we see the same markings on the bus as in the first shot, so we know it's the same bus. (00:22:05)
Visible crew/equipment: After the shots of the kids arriving on the first day of camp, when it cuts to Prue and Phoebe in the car, we can see the reflections of the camera operator and camera dolly on the surface of the car. (00:22:35)
Continuity mistake: When Prue leaves Buckland's, she's wearing a red tank top, but when she arrives at Camp Skylark, her shirt is different, both in style and color. She can't have stopped to change, because it's mentioned she left the auction house and headed directly to the camp. (00:07:00 - 00:09:20)
Continuity mistake: As soon as the water demon enters Sam, we can see that Prue's hair is completely dry. Then when she flips the switch to electrocute Sam to kill the water demon, her hair goes from dry to wet without ever coming into contact with any water. (00:36:25)
Other mistake: After Sam uses the powder on the sisters, erasing their memories, they're visited by Leo who starts to say "he must have gotten the powder" and one of the sisters finishes with "our mother." But in a later episode we learn all white lighters have this powder.
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