Mrs. Schachter sees the flames and smells the smoke during the journey. She foresees the dreadful future for every person on the train. Perhaps, the woman is the only one who understands the ending of the journey. While other people try to ignore the horrible truth, Mrs. Schachter understands it, and this is why she goes through the breakdown so early.
Detailed answer:
On the train on the way to Auschwitz, Mrs. Schachter is separated from her beloved spouse and children. This event becomes a trigger for her to break down. Firstly, she moans, and then her sobs and screams became hysterical. At night she stands in the middle and yells to nothingness about flames and fire.
It is an enormous struggle for her to lose her family. Everybody has a moment that appears to be too difficult to carry. Mrs. Schachter is the first victim of the new regime. She loses her mind because she cannot bear the sufferings and emotions she experiences.
Eventually, her screams about flames and causes panic in the train. Wiesel and other prisoners see her as a madwoman now. Her personality has been broken down. Moreover, some men beat her to make her shut because of her desperate screams and hysteric behavior. Other prisoners try to explain her behavior, but they do not realize the truth yet. Their explanations attempt to soothe their minds. Prisoners do not want to face the new reality.