Grandma Cosma is the wife of Grandpa Gonzo, the mother of Papa Cosmo, the mother-in-law of Mama Cosma, the grandmother-in-law of Wanda, and the paternal great-grandmother of Poof. She is the matriarch of the Cosma family, being in the first generation. She may have green hair, as this is the main attribute of the family.
Little is known about her because she has never been seen or mentioned.