Why won't the other Jews believe Hannah when she tries to tell them what is going to happen?

They believe that Hannah is sick after the deaths of her parents. Emotionally sick....

"She has been this way ever since she arrived, Fayge," Shmuel said, shaking his head. "Sometimes she is lucid, other times she talks of Rochelles and needles and snakes." He tapped his finger to his forehead. "It is the
sickness, I think. And the loss of her parents. Now she talks of the future."

The Rabbi was shocked and unbelieving of the sheer numbers Hannah spoke of....

"The men down there," she cried out desperately, "they're not wedding guests. They're Nazis. Nazis! Do
you understand? They kill people. They killed—kill— will kill Jews. Hundreds of them. Thousands of them.
Six million of them! I know. Don't ask me how I know, I just do. We have to turn the wagons around. We have
to run!"
Reb Boruch shook his head. "There are not six million Jews in all of Poland, my child."
"No, Rabbi, six million in Poland and Germany and Holland and France and ... "
"My child, such a number." He shook his head and smiled, but the corners of his mouth turned down instead
of up.