The girl in the red coat is not a character in the movie and has no specific symbolic meaning. She appears only for a moment and is never identified or given a backstory.
The scene itself is likely meant to highlight the brutality and dehumanization of the Nazi regime, as the bright red coat stands out starkly against the drab and oppressive surroundings of the ghetto. It could also be seen as a symbol of innocence and hope lost amidst the horror of the Holocaust.
However, it's crucial to remember that this is just one interpretation, and the scene's meaning is ultimately left open to the viewer's own understanding.