Mrs. Zzywicz is the mother of Kearney.
She has appeared in some episodes of the series, and was mentioned several times. In "I, (Annoyed Grunt)-Bot", Kearney mentioned that she is a stripper. In "Husbands And Knives", Dolph mentioned that she takes depression medication that makes her bloated, causing Kearney to tell him to shut up and he, Dolph and Jimbo punch each other. In "Oh Brother, Where Art Thou?", Kearney mentions that his parents now meet once a year when the prison and the asylum have their annual mixer; however he says nothing about them actually being divorced.
Given the supporting evidence it seems that Kearney's mother is currently in an asylum.