Lee made her first appearance as a featured singer in labelmate Infinite's debut studio album Over the Top on the song "Crying".

[4] On January 18, 2012, Lee released her second single "She's a Flirt", a duet with fellow Woollim Entertainment trainee, Yoo Ji-a.

[6] The group's debut studio album Girls' Invasion was officially released on November 17, along with its lead single titled "Candy Jelly Love".

[9][10] Later, Lee confirmed that although the members are signed under different agencies, they still have desire to promote and release albums together as Lovelyz in the near future.

[11] On November 17, Woolim Entertainment officially stated that Baby Soul has decided to begin using her given name Lee Su-jeong for her future promotions.