Mrs. Brisby's entire story arc is one giant CMOH. Not once in the entire film does she put herself before her family, especially her poor sick son Timmy, for whom she repeatedly risks her life in an effort to save his. The best part is that, throughout the whole ordeal, she remains terrified and fragile every step of the way, clearly showing that she would never in a million years have done what she's doing, without hesitation no less, had it not been for the sake of her own children. Her mantra for the movie: "Remember Timothy".
Jeremy retrieving Timmy's medicine packet. He did this while his life was at clear risk from Dragon, all the while having no idea how important it really was. To most people, it's just a scrap of paper. He went through all that trouble for seemingly no reason at all. Great guy.
Mrs. Brisby is in tears at losing the medicine, and her sheer joy when she sees that Jeremy got it is wonderful.
With some hindsight, quite a few of Auntie Shrew's actions are rather heartwarming.
The Shrew is set up to be arrogant and condescending, and not the most likable or pleasant person. Then when she sees Mrs. Brisby run off to sabotage the tractor while it's running, Shrew doesn't hesitate at helping.
When moving day comes earlier than expected, she's the one going around to all the animals in the field and warning them the plow is about to start.
She shows genuine concern when she hears Timmy is sick, she doesn't hesitate to help Mrs. Brisby stop the tractor, and when Jeremy tries to approach the Brisby home, Auntie ties him up when she thinks he might be threat to the children.
It's also implied that she's the one who is watching Mrs. Brisby's children while their mother is away and is clearly ready to go Mama Bear to defend them, even when Martin is a brat to her.
And even when she's ignoring Cynthia's statements about Timmy being sick, she does speak rather softly towards Cynthia by calling her endearing terms like "dearest", "dear" and "my pet." In spite of her abrasive personality, she really does mean well.
The "Flying Dreams" lullaby.
NIMH has quite a few heartwarming moments concerning Jeremy. This crow has no real reason to help Mrs. Brisby (unlike the others, he has no knowledge of Jonathan), but he constantly endangers himself, even attacking Dragon directly to rescue her at one point. And his transparent but well-intentioned attempts to allay her fears of The Great Owl later.
Mrs. Brisby: Owls EAT mice! Jeremy: Uh...Only after dark.
A small moment from Mrs Brisby. After Mr Ages is horrified at the death of Nicodemus, Mrs Brisby immediately lets him cry into her shoulder and comforts him. This woman is a true All-Loving Hero.
At the end, when Mrs. Brisby mentions that Justin became the leader of the rats.
It’s also worth mentioning how Mrs. Brisby entrusted the Stone to Justin as well. This considering that when she was initially given the Stone by Nicodemus, he mentions that her late husband had crafted it for her.
Speaking of Justin, the unadulterated respect he shows Mrs. Brisby, being Jonathan's widow, certainly qualifies.
Mrs. Brisby apologizes for coming “at a bad time” when Justin explains to Mr. Ages about Jenner stirring trouble, only for Justin to quickly reassure her their issues are not her fault. Then when they’re before the council, Justin along with Mr. Ages vouch for her and encourage the council to help Jonathan’s widow and her family as the least they could do for all Jonathan has aided them.
When Mrs. Brisby volunteers to be the one to drug Dragon’s food dish to help the Rats, something her late husband used to do, Justin tells her she doesn’t have any obligation to do so and expresses concern against it (understandably so, as Jonathan had recently died to Dragon and Mr. Ages having broken his leg). However when Mrs. Brisby insists and Nicodemus allows her, Justin is supportive of her choice and is the one to accompany her on the task and coach her through how to do it.
The moment near the end where Jeremy the Crow finally meets the one True Love he has been longing for the entire movie (and she's a female version of him) is another moment of sheer awww.
Little Timmy wants out of bed, while his mother isn't having any of it.
Timmy: Momma, I'm tired of bed, I wanna get up! Mrs. Brisby: Well... you're not getting up.
The film's happyending. Besides Jeremy finding his dream girl, the Brisby family and the rats are safe at last.
Though Mrs. Brisby's first name is never mentioned in the film, it's generally accepted by both the movie's fans and Word of God that her first name is Elizabeth, in honor and memory of her late voice actress, Elizabeth Hartman.
