Like Clyde's therapist, Dr. Lopez, Gayle has yet to make a physical appearance in the show.
She is first mentioned in "Get the Message", in which Clyde uses one of her perfumes.
In "Along Came a Sister", Clyde brings Lincoln a casserole that she made (or one that Clyde made from a recipe that belonged to her) to Frank's "funeral", telling him that she believes there's no greater comfort in times of grief than casserole.
In "Lincoln Loud: Girl Guru", Clyde tells Lincoln that his Nana believes that you shouldn't trust people who don't like chocolate while they were attempting to make chocolate pies for a school project.
In "Snow Way Down", it is revealed that Clyde's Nana's name is Gayle when Harold asks to call her in order to help him, Howard, and Lincoln off the ramp of insanity.
She was mentioned in "Teachers' Union", and it was revealed that she has a dog named Bingo.