They should have the little girl look at photos of missing African-American girls of that age, from that time period, in those areas, and see if she finds her "friend." Then they could see if the connection pans out. Not only would it not hurt in a case with few leads, it might go a long way to proving that ghosts exist.
A problem though is that the little "ghost girl" said that someone chopped her up and put her in the floor. The evidence on the bones indicates that they were placed outdoors first and were probably carried in by a rodent.