She first appeared in "Harold's Kitty" where she is the owner of a kitten named Thurston. Harold bangs sticks on Mrs. Ryle's property, which angers her. She throws water on Harold's head when he disrespects her wishes to stop banging on her railing. Harold eventually finds her kitten that has somehow gotten lost and became extremely attached to it. When Ms. Ryle appeared to get Thurston back, Harold wouldn't give the cat up. In a bizarre turn of events, the problem escalates into a hostage situation; Harold barracades himself inside his house with Thurston. Arnold eventually is able to calm Harold down and convince him to do the right thing.
It is unclear how the relationship between Harold and Ms. Ryle turns out. Harold calls her a "mean old lady" and in turn, Mrs. Ryle thinks he is a "rotten kid". In the end of "Harold's Kitty", Ms. Ryle allows Harold to come over her house to play with Thurston every once in a while. It is unknown whether Harold and Mrs. Ryle ever reconsciled their differences and became friendly or if they just learned to tolerate each other.