Elizabeth Brisby was born a mundane mouse on the Fitzgibbon Farm at some point before 1982. When the first Uplifted Rats, freshly escaped from NIMH, found their way to the Farm, they psychic waves progressively heightened her mental abilities, and Brisby was all the more responsive to them due to her high capacity with the Power.
Her fundamental goodness and her heightened intelligence, along with her attractive appearance, were enough to raise the interest of Jonathan Brisby, a fullu Uplifted mouse. Despite the Rats of NIMH's disapproval of Jonathan's relationship with a "lower" creature, the two developped a loving relationship, eventually coming to think of themselves as husband and wife. In a positive feedback loop, this closeness with Jonathan caused Elizabeth's intelligence to improve even further, making her nearly the equal of the biologically-uplifted Rats and of Jonathan himself.
Overjoyed with his beloved's improving capacities, Jonathan, according to the advice of his friend and mentor Nicodemus, began teaching his wife various skills, among them the ability to read. However, worried about Elizabeth's reaction to the fact that he would age at a much lower rate than her, he refused to tell her about his origins and his ties to the Rats of NIMH. Jonathan and Elizabeth had three children, Martin, Theresa and Timothy.
Jonathan's Death and Later LifeEdit
Eventually, Jonathan was killed by the cat Dragon, without Mrs Brisby ever knowing what had happened to him. She was, at that point, carrying one last child, Cynthia. Brisby was never the same after Jonathan's death, but made do, successfully protecting her family against the hazards of the Field. In 1981, she moved her family to a safer house: a hollow block of concrete in the middle of the Field.
In 1982, her son Timmy fell ill. After consulting Mr Ages, Brisby was told that Timmy couldn't be moved from his bed for three weeks. This was a tragedy, as Moving Day was drawing nearer and the Brisby House would surely be destroyed by the plough. On the common advice of Auntie Shrew and a crow called Jeremy, she visited the Great Owl, despite the immense danger this represented for a mouse. Impressed by this show of bravery and the fact that she was the widow of Jonathan Brisby, the Great Owl sent her to the Rats of NIMH.
Meeting the Rats of NIMHEdit
At the Rosebush, she was almost killed by Brutus before she ran into Mr Ages, who led her to Nicodemus. The elderly rat had been expecting her visit, thanks to having observed her every move using the Spinner. He revealed the secret of the Rats of NIMH to her, told her the truth of her husband's death, and gave her one last heirloom from him, the Amulet.
Captivity in the Fizgibbon HouseEdit
As repayment for the Rats' promised help in moving her house to the lee of a large stone, she offered to be the one to drug Dragon, the very task that had caused the death of Jonathan. She succeeded in feeding the sleeping powder to the cat, but was captured by the farmer's son, Billy, before she could escape. Fortunately, as Brisby was naked (Justin had advised her to remove her cape, lest it get caught on something), Billy remained oblivious to Brisby's status as an Uplifted rodent, and simply decided to make her his pet. During her captivity, Elizabeth overheard a telephone call that revealed the imminent arrival of NIMH employees to exterminate the Rats of NIMH.
Saving her ChildrenEdit
Elizabeth escaped her cage just in time to warn the Rats against NIMH. However, she arrived to find her house sinking in a mudhole, with Nicodemus dead and Jenner threatening to take over. Jenner saw the Amulet and threatened to steal it, but was fortunately killed by his former ally Sullivan after duelling Justin. Meanwhile, having unlocked her inner courage, Brisby was able to use the Amulet to pull her house out of the hole and move it to the lee of the stone.
Little is known about Mrs Brisby's later life. Due to not having received the serum that Uplifted her husband, she aged faster than her own children, and was alreayd a gray-haired, glasses-wearing old lady when she saw her son Timothy Brisby leave for Thorn Valley.
Differences with the NovelEdit
Mrs Brisby's counterpart in the novel is called Mrs Frisby — the name had to be changed for the film due to a copyright problem. She is generally similar to her movie counterpart, but does not wear a cape. Analysis of her behavior has also shown that Frisby was generally more assertive toward other characters than Brisby is shown to be in the film.