On April 19, 2012, Girl's Day made a comeback with the mini album Everyday II. The album included the song "Telepathy", which was composed by Sojin. On the same year, Sojin and a male composer wrote the song "It's Snowing" for Tokyo Girl. The song was later released on December 7.
2013–2016: Collaborations and Family Outing OST
On March 14, 2013, Girl's Day released the full-length album Expectation. Sojin wrote the intro song "Girl's Day World", and co-wrote the lyrics for "I Don't Mind" with her fellow members. On October 15, Girl's Day released the song "Let's Go", written and composed by Sojin.
On March 2, 2014, Sojin collaborated with hip hop artist Crucial Star on a remake of Park Hye-kyung's song "Three Things I Want to Give You".