Greg's great-grandmother and the head of the Heffley family, only appearing in The Ugly Truth, as a minor character . She also has Legos that Susan bought to let her kids do something there. Gammie glued them together because of mess. Gammie is a trickster and knows a lot because of "experience". When someone in the family is about 12 or 13 years old she gives them the Talk, which is about how kids should not be hurrying to grow up.[11]
According to the extended Do-It-Yourself Book, Gammie is Susan's grandmother and Gramma's mother-in-law.But she appears to be more likely on Frank's side because whenever there are any "Heffley Family Reunion" Frank's brothers and grandpa also appears there.

Gammie