This woman is the mother of Donnie, Penny's ex-boyfriend.

She is mentioned in "The Boyfriend Complexity" when Penny's father Wyatt tells Leonard about Penny's ex-boyfriends. Donnie was mentioned as a genius and a rocket scientist who was gonna make millions turning farm waste into biofuel and selling it to the government. Then she was mentioned when Wyatt says that all her son did was mix pig poop with a little water and then he pumped it into her Camry.