She will probably never appear again since it was just Clamantha dressed up as her. However, you could see her in the opening theme, sitting down in the audience next to Steve Jackson at Bea`s audition. What`s odd is that Clamantha, who is Doris, is seen in the audience too, so it is unknown if it is her.
However, Clamantha could be secretly controlling her Doris costume like a puppet.
When Clamantha is cutting Shellsea's picture out of the yearbooks in Fish Talent Show, Doris` picture appears in one of them. This could be Clamantha (as Doris) merely having her picture taken.