What happened at the marketplace that eventually change mrs frisbys life forever?

Answer 1

Nicodemus informed Mrs. Frisby how her husband (Mr. Jonathan) had been captured as part of the Nimh organization, and how he died trying to help the rats who had escaped (putting sleeping powder into Dragon's bowl). This changed Mrs. Frisby's life because she was more knowledgeable about her husband's mysterious death. She was in tears when Nicodemus told her about this

Answer 2

Mrs. Frisby encountered the Great Owl at the marketplace, who advised her to seek the help of the rats in moving her home to ensure her family's safety. This encounter led to Mrs. Frisby becoming involved in a complex and dangerous plot involving the Rats of NIMH and ultimately led to the saving of her family and a new beginning for them.