Kathryn Raio is a composer who was been working on Sesame Street since 2008, her first season being season 40. She has written several songs for the show, usually co-composing with JP Rende.
She has also written songs for some Sesame products, including Let's Rock Elmo and Elmo's Tickle Hands, as well as a song by Rosita and Elmo in a PSA for Flu.gov. (YouTube)
Raio also provided background vocals for the song "Puppet Man" for the documentary, Being Elmo: A Puppeteer's Journey.