Why was the seamstress who lived in Vladek's building arrested?

Vladek is recounting to Art the story of what happened not long after he married Anja, Art's mother. While walking home one night, he learned that a local seamstress had been arrested for storing Communist documents. Under the Nazis, this was a capital crime as the regime would tolerate no opposition whatsoever. The seamstress had been given the documents to hide by Anja, who knew she would get into serious trouble if the Nazis found them in her apartment.
She'd been translating Communist documents into German for the boy from Warsaw, who was involved in subversive activities. When she got wind that the police were coming to search her apartment she asked the seamstress to hide them. The seamstress was arrested, but she was released after three months. During that time, she never breathed a word to the police about Anja, largely because Anja's father had paid her to keep her mouth shut.