NEW YORK — Amy Krouse Rosenthal, a prolific and free-wheeling author, filmmaker, and speaker who brightened lives with her wide-eyed spirit — and broke hearts when she wrote of being terminally ill and leaving behind her husband, Jason — died Monday at age 51.

Ms. Rosenthal had been diagnosed in 2015 with ovarian cancer.

She ‘‘was the most life-affirming person, and love-affirming person,’’ said her longtime literary agent, Amy Rennert. Fellow author John Green tweeted: ‘‘She was a brilliant writer, and an even better friend.’’

A Chicago native and longtime resident and Tuft University graduate, Ms. Rosenthal completed more than 30 books, including journals, memoirs, and the best-selling picture stories ‘‘Uni the Unicorn’’ and ‘‘Duck! Rabbit!’’ She made short films and YouTube videos, gave TED talks, and provided radio commentary for NPR, among others.

She also raised three children and had a flair for random acts of kindness, whether hanging dollar bills from a tree or leaving notes on ATM machines.

‘‘I do what feels right to me. If it resonates or plants some seeds, great,’’ she told Chicago magazine in 2010.

While her books were noted for their exuberant tone, she started a very different conversation early this month with a ‘‘Modern Love’’ column she wrote for The New York Times. Ms. Rosenthal told of learning about her fatal diagnosis, and, in the form of a dating profile, offered tribute to Jason Brian Rosenthal, her husband of 26 years. The essay was titled, ‘‘You May Want to Marry My Husband.’’

‘‘If you’re looking for a dreamy, let’s-go-for-it travel companion, Jason is your man. He also has an affinity for tiny things: taster spoons, little jars, a mini-sculpture of a couple sitting on a bench, which he presented to me as a reminder of how our family began,’’ she wrote. ‘‘Here is the kind of man Jason is: He showed up at our first pregnancy ultrasound with flowers. This is a man who, because he is always up early, surprises me every Sunday morning by making some kind of oddball smiley face out of items near the coffeepot: a spoon, a mug, a banana.’’

‘‘I am wrapping this up on Valentine’s Day, and the most genuine, non-vase-oriented gift I can hope for is that the right person reads this, finds Jason, and another love story begins,’’ she added.

The column has drawn almost four and a half million readers online.

Her husband said in a statement afterward, “When I read her words for the first time, I was shocked at the beauty, slightly surprised at the incredible prose given her condition and, of course, emotionally ripped apart.’’

Ms. Rosenthal worked in advertising for several years before she had what she called a ‘‘McEpiphany’’: She was with her kids at McDonald’s when she promised herself that she would leave advertising and become a writer.

What she described as her plastic fork in the road led to countless dead ends, however, until she published “Little Pea,’’ about a pod denied his favorite dessert (spinach) until he finished all his candy (which he detested). The book received favorable reviews.

“For all I know, she may suffer torment upon torment in front of a blank screen, but the results read as if they were a pleasure to write,’’ Bruce Handy said of her work in The New York Times Book Review in 2009. “Her books radiate fun the way tulips radiate spring: They are elegant and spirit-lifting.’’

Ms. Rosenthal regularly published at least a book a year and sometimes three or four. Rennert said Monday she had completed seven more picture books before her death, including a collaboration with her daughter, Paris, called ‘‘Dear Girl.’’

Ms. Rosenthal loved experimenting with different media and blending the virtual and physical worlds. One of her favorite projects began with a YouTube video, ‘‘17 Things I Made,’’ featuring everything from books she had written to her three children to a peanut butter and jelly sandwich to a mess in a kitchen sink. At the end of the video, she welcomed fans to join her at Chicago’s Millennium Park, on 8/8/2008 at 8:08 p.m. The goal was to make a ‘‘cool’’ 18th thing.

Hundreds turned out to ‘‘make’’ things — a grand entrance, a new friend, a splash, something pretty.

‘‘I tend to believe whatever you decide to look for you will find, whatever you beckon will eventually beckon you,’’ she said during a 2012 TED talk.

Material from The New York Times was used in this obituary.