The actual size of this portrait is about the same as an average photobooth pic, being 38 x 57 mm. I imagine it is a miniature print done by the studio that took the original photo. It doesn’t appear to be a later copy. The long-tressed, serene young lady is wearing black but I don’t think it is necessarily for mourning. I have seen similar photos labelled as being a souvenir of the Sacrament of Confirmation in the Catholic church.
You can see what is written on the back in pencil. Good luck to anyone who is game enough to try to decipher it. All I can make out is Lili, possibly Castein and Albert but even then I’m not sure I have any of it right.