whats the connetction with elie and the french girl at the train station

Elie meets a young French Girl at a train station who wipes the blood from his forehead and offers him some comforting words.

The French girl tells him to keep his anger for another day. Years later in Paris, Elie Wiesel runs into her in the Metro. She actually turns out to have been Jewish.

Actually to be specific, Elie is beaten at a warehouse. That's when the French Girl, passing as an Aryan, helps Elie. He met the girl many years later after the war at the train station (metro). That is when he finds out she was really Jewish, although Elie had his suspicions.