After the Rats move Mrs. Frisby's cinder block house out of the path of the plowers, she watches in safety while the fields are plowed. After that, with Timothy well enough to move, they cover over the entrance and walk to the brook where they and other mice live during the summer. While collecting moss, she meets up with a neighbor:
...she saw one of her neighbors, a lady mouse named Janice who, like herself, had four children. Janice ran over to talk to her.
"You're so late getting here," she said. "We all thought something must have happened to you."
(O'Brien, Mrs. Frisby and the Rats of NIMH, Amazon.com)
To keep the secret of the Rats, Mrs. Frisby claims that her cinder block was safe the whole time, and Janice accepts that as luck. Janice, like other minor characters, is more concerned for her own well-being, and is only a little surprised to see Mrs. Frisby alive and well; Janice's impact on the novel is mainly to convince Mrs. Frisby that while she has to keep her secrets from the other mice, she should tell her own children, who deserve to know how the Rats helped to save their lives.