Food, Lies and Videotape - S3-E17
Continuity mistake: Towards the beginning, Carl enters with a new video camera and we see a regular view of the scene mixed with POV shots from the camera as Carl narrates. When he's standing at the door with his bag, in the POV shots from the camera you can see that the door is open, but in the wide shots, it is closed.
Answer: It is said that as Steve Urkel became a more popular character on the show, Judy became less important to the storylines, plus either her or her parents were demanding more money, causing her to be removed from the show entirely.