Horikita was one of the six female celebrities taking turns to host "Girls Locks!", a segment of the Japanese radio program "School of Locks" from the radio network Tokyo FM. When she was the host, Horikita provided book recommendations to her listeners and called selected letter-senders to discuss the questions they wrote in their letters. Her stint was at ten in the evening, every third or fourth week of the month. She took turns with Erika Toda, Yui Aragaki, Chiaki Kuriyama, Nana Eikura, and Kii Kitano until she left the program in 2009.