To the people who actually know what goes on in these situations this story is not news. The interest in it is like people rubbernecking a car accident. Really you should move along - there is nothing to see here.
The most likely story is as the people in the camp have reported themselves, they bought the child from or were handed the child by Bulgarian itinerant workers who couldn't afford her upkeep. People living on the edge are doing as they probably always have done, just another mouth to feed and a bit of income to be made.
Remember Greece is suffering at the moment and a heartwarming anti- Roma story can't hurt. This was one of the ways Hitler kept his people on side when Germany was suffering.