Mrs. Krabs was or is the mother of Pearl Krabs and the wife of Eugene H. Krabs. In a book, Mr. Krabs states that Pearl takes after her mother, though this cannot be taken into account since the SpongeBob SquarePants books are not canon to the series. read more
Pearl's lack of a mother is a reference to the phrase "mother of Pearl," which Mr. Krabs often says when something surprises him. Stephen Hillenburg is against revealing the identity of Mrs. Krabs and has kept it a secret throughout the series. read more
The show never references her, but a book mentions that she is Pearl’s mother. At one point, Mr. Krabs clearly states that “Pearl takes after her mother.” I don’t think that’s the full story. read more