Dwarf Hamster Male/Female?

OK, Out of 7 of my dwarf hamster pups, there are 5 girls, 2 boys. One of the "supposed" girls is difficult for me to tell her private area looks different than the other pups? The girls have 2 openings already, the is clearly visible, the boys well lets just say i know!! As for this special one, who is also the runt my opinion is girl, but where's her l opening? could it be because she's a little under developed than the rest of her sisters?