User blog comment:Zathronas/Analysis by an author: Volume 2 episode 1/@comment-10390252-20140725123628/@comment-3146930-20140725203834

Also consider that Roman calls Emerald a street-rat. Add in that her last name isn't revealed, this could mean she doesn't have one. Now multiply that by a factor of her happiness at seeing Cinder and it seems that Cinder may have found her on the streets and brought Emerald into her group.