Katie is, of course the daughter of Bill McLaughlin, who it seems spends most of his time stalking his neighbor, Mary Tibaldi-Hubert.   Bill is relentless in his quest fo convince Mary (could've sworn Ben Guerrini used to call her Marianne) that is was not he, but Robie Wood that put the whoppie cushion on Miss Tibaldi's chair before that Math test in February, 1966.  (Sure Bill, as if Robie would EVER pull a stunt like THAT!).  Mary simply wants to put the whole episode "behind her".  

Lloyd Diehl put the pieces together to conclude that Bill and Katie  are a father/daughter duo.