Why did yetta think that she and mr. bernstein were on the same side

Yetta thinks that she is on the same side with Mr. Bernstein because they acted in the same manner when trying to save the girls from danger. That means, they took similar action and had the same goal in mind when trying to save the girls.

Below is an excerpt:

"He was only slapping the hysterical girls, like Yetta had done with the girl who'd fainted. He was trying to save their lives.

We are on the same side now, Mr. Bernstein and me, Yetta marveled."

Explanation:

When the fire broke out in the building, Mr. Bernstein was hurrying the girls to leave the building as soon as possible. In trying to get them out hurriedly, he slapped the girls; a similar action Yetta took when a girl fainted.

"Uprising" is a story by American author, Margaret Peterson Haddix. The story reveals the outbreak of a fire in a factory which led to the death of Jane, Yetta and Jacob; only Bella survived. The outbreak was considered is considered as the worst workplace disaster in history. In the story, Bella now recounts the incidence to her two daughters.