In Night by Elie Wiesel, who did Elie meet years later on the Paris Metro?

Elie often works next to a young French girl in the warehouse; he has a sense of trust in her, although he speaks no French and she seemingly speaks no German. Elie really has suspicions that she is Jewish, but she has official papers that declare her Aryan. She is a forced labor inmate.
After Elie suffers an especially difficult beating one day, he feels a "cool hand wiping [his] blood-stained forehead." The French girl is smiling at him sadly and doing what she can to help Elie recover. To his surprise, she then slips him a piece of bread and hesitates, looking deep into his eyes as if making a decision. Finally she speaks in nearly perfect German:

Bite your lips, little brother . . . Keep your anger, your hate for another day, for later. The day will come but not now . . . Wait.

This is the same (grown-up) girl he meets on the Metro years later in Paris, and they both recognize each other.
She explains that when hostilities rose, her family determined that she could pass herself off as Aryan, and this is how she had acquired the papers that spared her from a concentration camp. She couldn't risk anyone knowing that she spoke German, as it would have created suspicion. However, she tells Elie that she "knew [he] would not betray [her]" when she spoke to him that day.