Continuity mistake: When Mrs McCluskey is talking to her sister on the coach, she has a plate of food in her left hand and some papers in her right. When Roberta rips the papers out of her hands, the plate of food is gone and is replaced by a sandwich.
Audio problem: When Lynette warns Anne to never lay a finger on her son Porter again, from behind Lynette's head she is still talking, but no words are coming out.
Audio problem: When Lynette slaps Anne Schilling across the face in the wash room, a slapping sound can be heard after her hand goes past Anne's face.
Continuity mistake: When Lynette gets up from the PTA meeting to go to the washroom, she has a purse on her shoulder. After her confrontation with Anne Schilling, Lynette storms out of the washroom but she is no longer carrying her purse.
Answer: Kayla was sent away in episode 16 (The Gun Song) in season 4, after falsely accusing Lynette of child abuse. She now lives with her grandparents - probably Nora's parents.
I'm curious why we never see her again, why she never talked about, and why Tom never mentions visiting her.