She has never made an appearance in the show, nor has her name been revealed, but she was mentioned in Blondas Have More Fun! by Wanda, who said to Blonda, "Mom always liked you best!". She is possibly divorced from Big Daddy, as in the episode Big Wanda, he is shown living alone and entering in a relationship with Mama Cosma.
Another time she was mentioned in another episode in "A Fairly Odd Christmas", when Cosmo said "I never been that scared since Wanda's mother moved in with us".
She was also mentioned in Force of Nature when Cosmo talks about how when he put garbage under his pillow, someone would wake him up, force him to take out the trash and then complain about him to her mother, with the implication that he's talking about Wanda.