Continuity mistake: Season 2, Episode 17: "Could I Leave You?" - When Mr. Beale throws a pencil into his mug, the pencil can be seen on his desk in the shot immediately afterwards.
Audio problem: Season 2, Episode 17: "Could I Leave You?" - Veronica's son's lip movements do not match when he tells her that he's thirsty.
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.