She is a member of the Z of the Month Club and her usual delivery is instead sent to Telly Monster. The two converse over the phone, where he learns she has his package from the Triangle of the Month Club. She tells him she'll come by to pick it up following her zither lesson. As the day passes, Telly grows fond of her letter Z and likewise, she finds his triangle very interesting. Once they meet up, they find it hard to part with the objects and start making plans to hang out, so they can each play with triangles and Zs.
According to the phone book in Hooper's Store, she lives on Zanzibar Street and her phone number is 555-3805 (referencing the show number).