In the episode where Sabrina and Libby bump into each other and Sabrina becomes mean and Libby becomes nice and when Sabrina and Salem try to take over the world.

If you watch the part when the bump heads at school the camera shows Sabrina and her hair is in a bun low on her head and is perfect,then they turn to Libby, when they turn back to Sabrina her hair is lopsided and very messy. When Libby apoligizes a couple of seconds later they turn back to Sabrina and her hair is perfect again the way it started.

WHOOPS