Why was Mrs. Frisby a widow?
In the book Mrs. Frisby and the Rats of NIMH, Mrs. Frisby's husband was one of the original animals that had been collected for experimentation in the labs of NIMH. Mrs. Frisby goes to find some help for her family in order to move heir home. She is introduced to Mr. Ages and later to Justin and the other rats that have escaped from NIMH.
The rats have an idea as to how to help Mrs. Frisby but it includes having to put the farm cat named Dragon to sleep. They explain to her that Mr. Ages usually does it but he broke his leg trying to get away from the cat the last time. She volunteers to be the one to put the sleeping powder in the cat's food.
Mrs. Frisby is then told that her husband died trying to complete the same process.
"And it was in doing the same thing, last year, that your husband died." (95)