Cornflower Fieldmouse was the daughter of Mr. and Mrs. Fieldmouse, wife of Matthias, mother of Mattimeo, the grandmother of Martin II, and mother-in-law of Tess Churchmouse. She was a skilled cook and often wore headbands.
Before the Late Rose Summer Wars, Cornflower and Matthias, inspired by Abbot Mortimer, search Redwall Abbey to find Abbess Germaine's Warrior's Code. After solving a series of riddles, the pair successfully locates it.
When Cluny the Scourge arrived, Cornflower was a great help to Redwall, and was able to fend off the rat during one of his attacks. She threw a lantern onto his siege tower, which caused it to burst into flames. Although she was known to be a quiet mouse, she would speak to Matthias and once helped him through his self-doubts and gave to him her favorite headband as a sign that she believed in him.
When Redwall was under attack by General Ironbeak during the Summer of the Golden Plain, Cornflower was very helpful in figuring out the riddle. She helped take care of and comfort Rollo after his mother died. She often missed her husband and her son and would reminisce with Mrs. Churchmouse. When General Ironbeak and his flock came to conquer Redwall, she was amongst the many creatures that helped defend it. She also came up with an idea to dress up as the ghost of Martin the Warrior; she wore Matthias' battle armor while Constance spoke in a loud terrifying ghost voice to scare the superstitious birds. Her plan worked, and the villains became extremely frightened. She would have continued her masquerade, but Abbot Mordalfus told her to stop because she could be killed if Ironbeak and his birds were to uncover her plan.
She obeyed her Abbot and asked if Constance could return the armor to the gatehouse. Later that night when Ironbeak and his flock infiltrated the barricade, the Redwallers were rudely awakened. Before Ironbeak could take his revenge on the dwellers of Redwall, she witnessed Constance and Stryk Redkite attack the rooks and crows. Stryk and Constance both slayed Ironbeak and his seer Mangiz.
After the war with Ironbeak had ended, she waited for the return of Matthias and Mattimeo for half a season. After she was reunited with her family and friends, she helped and attended a feast for the heroes’ return.
Redwall TV Series
Cornflower is described as a fieldmouse in the book. In the Redwall TV Series, her father is John Churchmouse instead of Mr. Fieldmouse (who does not exist in the TV series). This discrepancy poses an interesting situation. If Cornflower was a Churchmouse, then Tess Churchmouse would be her sister. Tess marries Mattimeo, who is the son of Cornflower and Matthias. This would mean that Mattimeo and Tess married their aunt and nephew, respectively.
This makes Cornflower's heritage in the TV show more likely to be a mistake. In the second season of the TV series, the fact that Cornflower is the daughter of John Churchmouse no longer seems to be canon since she refers to him by his name in lieu of as her father.