Sally the Crab is the grand-aunt of Eugene H. Krabs, who is mentioned in the episode "SpongeBob SquarePants vs. The Big One" and the commentary of the special, "Plankton's Special Sinister Commentary."
When she was in high school, she dated the Flying Dutchman.
She is mentioned in the episode "SpongeBob SquarePants vs. The Big One" and the commentary of that episode, "Plankton's Special Sinister Commentary," in the same scene. In the former, Mr. Krabs tells the Flying Dutchman to let Cashy go, and in return, never soil his waters again. He says he promises on Sally's false teeth, but the Flying Dutchman calls him a liar because Sally does not actually wear false teeth. Mr. Krabs asks how he knew that, and the Dutchman says he dated her in high school.