All I could find till now is that there is a ballet called Coppelia and the story of the ballet is about a dr. Coppelius who creates a doll and calls it Coppelia. When you search for Coppelius you'll find some sites but nothing about the origin or meaning. I have to say though that the ballet (the music) was written by E.T.A. Hoffmann and this composer used to have a job as inventor of surnames for Jewish people, like Guldbaum and Apfelbaum (says a biography about him). It might thus be that he created the name Coppelius too, but how he created it is unclear to me.