I figured something like this was going to happen someday (private Facebook pictures going public). Since this friend "Sara" mentioned in the article has pictures of herself and Beatrice on her Facebook, anyone who's friends with Sara (not Beatrice) can see the pictures and sell them to the media, as they obviously did.
Also, though, the article mentions Beatrice's favourite books and movies listed on her Facebook profile. To see Beatrice's page, someone would actually have to be friends with Beatrice (or be part of a network she's joined). So it seems from this information that one of her "friends" betrayed her by spilling details of her Facebook page to the media.