I saw Yeardley Smith on Mama's Family.

I saw it today. The episode was entitled, "Where There's Smoke." In the episode Smith plays the role of Bonita Rokiki; an escapee from juvenile hall who almost ruins mama's chance of becoming president of a church club. She was using the voice she used in "Lisa the Simpson", where she daydreams about being overweight and having all those kids with Ralph Wiggum.