The Interview Show

Mrs. Garrett was missing from the majority of the back half of season six. This was the start of her "recurring character" status despite being in the credits. They'd essentially run out of stories for her, and even Charlotte Rae said the character had become boring. 

The times she does appear in the back half of the season, including this episode, are only in episodes that were actually recorded during the first half and aired out of order. This episode was recorded as the 12th for the season, but aired as the season finale. (Some context in the episode also gives this away.)