My explanation of the little girl
First I want to say that I thought this was an amazing movie!
People have had lots of threads created regarding questions about the little girl. I believe that this is the best explanation after giving it a lot of thought and reading a lot of the posts....
I believe that the little girl is the daughter that Hanna mentioned that was killed at the "brothel". I believe that Hanna became pregnant from the rapes and she was the woman that had to shoot her daughter (baby). If you think about it, with all the rapes, it is extremely likely that Hanna got pregnant. The soldiers would not have wanted to have any babies in the brothel and most likely they forced her to kill her own baby right after she had the baby. The soldiers must have had her shoot the baby (in that horrible manner that I won’t even mention!) immediately after the baby was pulled out of her body and because of the direction and part of the body that the baby was shot… (Babies usually come out head first) she "never saw her face" as she mentioned in one of the beginning scenes. I know this is a horrible scene to bring up but I am pretty sure this is what happened. Also Hanna mentions that “the woman” dies of sorrow. Her “friend” also dies, but of bleeding to death. It seems that “her friend” and “the woman” are aspects of herself that became submerged because of the horrors she experienced. I believe she has kept the little girl with her in her mind as she has gone on with her life. The little girl mentions at the beginning that Hanna dresses her in red corduroy and a blue jersey. In the last scene out the window you see Hanna’s 2 son’s running in the field. They are dressed in the red and blue just like she had envisioned her daughter dressing. I’m sure that this is reality now with her 2 sons…But it is included to indicate that she has come full circle and can now be at peace somewhat in that she can take care of her boys as she would have wanted to take care of her daughter who was so horrifically killed as an infant.
I want to add that if the soldiers put her baby on her belly with the infant's head facing the other way and Hanna was made to shoot the gun so close to her own face, it is likely that this is what caused her partial deafness. This was never explained beyond the fact that Josef asked her if she was born with her deafness and Hanna said no. The tone of Hanna's voice indicates that the cause was very traumatic.