It was unknown as to when the two girls first met, but it is implied that it happened before the events of the series, most likely as the Kittredges have been a client in the bank that Ruthie's father works in. She is depicted to have an affinity for princesses and fairy tales, most especially Andrew Lang's Fairy Books and Grimms' Fairy Tales, in contrast to Kit's more tomboyish personality - while the latter talks and raves about baseball, Ruthie cares little about Kit's favourite sport and reads fairy-tale books instead. Although this would be the reason for their occasional bickering and quarreling at each other, they do appear to be in good terms most of the time, as Ruthie would often help her friend write articles for a homemade newspaper they came up with.
Downfall Parody Universe
Ruthie first appeared in Kit Snaps and Kittredge recruits an Unterganger, although it wasn't until she made a formal debut in the Parody Universe. She serves as Kit's lackey and adjutant - her penchant for informing Kit incessantly got her into trouble, however.
There was even a time when someone, most likely Fegelein, Merriman or perhaps even Tuhkachevsky, abducted Smithens and stuffed her into a Günsche costume. Ruthie then informed Hitler about her situation, only to end up being yelled at.