Sometime in Season 3 because Quinn sees her baby for the first time since she was born. I don't think anybody except the people involved in the mostra know exactly when but definitely sometime soon :)
Shelby is set to return in Season 3. Her first appearance will be in the secondo episode, I Am Unicorn. She will be back as a biology teacher and cause trouble for Rachel, Quinn, Puck, and former flame, Will. ~ taken from link