When Karen Killilea was born in 1940, three months premature and weighing less than two pounds, few doctors expected her to live. She had sparkling eyes and an infectious smile but spent her first nine months in a hospital, watched over by nurses in the newborn intensive care unit.

Once she came home to Rye, N.Y., she seemed unusually still and rigid for an infant, never rolling over, kicking her feet or reaching her tiny hands toward her parents. Ms. Killilea (pronounced KILL-ill-ee) was eventually diagnosed with cerebral palsy, a group of movement disorders that led one physician to suggest her parents institutionalize her. Another declared that “in China, they take such children up on top of a mountain and leave them.”

Instead, her parents — James and Marie — vowed to treat their daughter like any other child. They took Ms. Killilea to more than 20 medical specialists in the United States and Canada before finding a doctor who recognized her intelligence and suggested a rigorous physical therapy regimen, helping her strengthen her limbs.

By age 8, she could walk up the stairs on her own, taking 20 minutes the first time. She wore a football helmet in case of falls and ultimately learned to swim and ride horses.

As she became more independent, her mother met with other families to share information about raising children with cerebral palsy. She traveled to the state capital to campaign for legislation supporting people with disabilities and in 1952 published “Karen,” a best-selling book about her family’s experience and one of the first to offer a detailed account of living with a severe physical or developmental disability.

Excerpted in Reader’s Digest and Ladies’ Home Journal, it was translated into at least 10 languages and earned Marie Killilea two Christopher Awards, given to books, films and television series that “affirm the highest values of the human spirit.” The Cerebral Palsy Foundation later credited “Karen” and a widely read follow-up, “With Love From Karen” (1963), with kick-starting an advocacy movement for people with cerebral palsy.

“You’ll want to read this book because it is a wonderful story of human courage, patience and triumph,” wrote physician and novelist Frank G. Slaughter, reviewing “Karen” in the New York Times. A Saturday Review book critic declared, “Anyone who meets Karen will postpone resigning from the human race.”

Ms. Killilea, who went on to train dogs and work for four decades at a retreat for Catholic clergy, was 80 when she died Oct. 30 at a nursing facility in Port Chester, N.Y. “As we say in the family, she wasn’t supposed to live eight minutes, let alone 80 years,” said her sister Kristin Viltz.

The death, from complications from a respiratory condition, was not widely reported until the Times published an obituary last week.

In the decades since “Karen” was published, Ms. Killilea and her family received more than 100,000 letters and responded to at least 15,000. Many came from parents who felt comforted by their story. Others were from readers who felt moved to build clinics, donate money or volunteer on behalf of people with disabilities, who were frequently scorned and segregated from the rest of society.

Ms. Killilea’s mother wrote that during their long search for medical advice, when Karen was still a child, they were thrown out of a tourist home in Kentucky by a woman who shouted that “only bad, dirty people would have a child like that.” As part of her advocacy efforts, Marie Killilea later co-founded Cerebral Palsy of Westchester, a regional nonprofit, and helped organize a national organization, now known as United Cerebral Palsy.

“If we hadn’t been involved, very soon there would have been others to work for the cerebral palsied,” she wrote in a 1983 foreword to “Karen.” “It was like a spontaneous combustion. Parents all over the country were in the throes of the agitation that brings the seed to flower.”

While Marie Killilea delivered speeches and appeared on television, Karen Killilea preferred to stay out of the spotlight, especially after visitors turned up at the family home unannounced, hoping to see or even touch her.

“She was fiercely independent and private,” said Viltz, her sister, “but to her friends, she was an absolute stitch,” telling jokes and stories. “When people made comments about how she was handicapped, she would say, ‘Oh, no, I’m not handicapped. I’m permanently inconvenienced.’ ”

The second of four children, Karen Ann Killilea was born Aug. 18, 1940, in Port Chester, a New York City suburb next to Rye, where she grew up. Her father worked for the New York Telephone Company, and her mother was a homemaker before devoting herself to disability rights advocacy.

Ms. Killilea learned to whistle before she could speak and was later nicknamed Wren, after a family of birds known for their small size but boisterous songs. (The name served as the title of a children’s book adaptation of “Karen” that Marie Killilea published in 1954.)

She expected no favors because of her disability, her mother said, and did chores just like her siblings, making her own bed and helping set the table. “That’s the important thing I should like to tell all parents of children with physical handicaps,” Marie Killilea told the St. Louis Post-Dispatch in 1952. “You can’t favor them. Don’t run to them if they start to fall. That implies the parent is afraid, and the children become fearful too. Hide your fear.”

Ms. Killilea’s mother died in 1991, followed by her father in 1994. In addition to her sister Viltz, of Hawthorn Woods, Ill., survivors include another sister, Marie Irish of Fairfield, Conn.; and a brother, Rory Killilea of Seattle.

With support from her sister Marie, Ms. Killilea studied at the Academy of Our Lady of Good Counsel in White Plains, leaving school when Marie went to college. She later lived independently in Larchmont, N.Y., where she worked as a receptionist at the Trinity Retreat House. By then, she had switched from using crutches to a wheelchair, which promised greater freedom.

“No more will I be a drab, slow little sparrow that hops around with his head down,” she told her mother after making the change, according to “With Love From Karen.” “I’ll be free, really free. I’ll be an eagle with my face to the sun.”

She later flew to Rome, twice meeting with Pope Paul VI, and continued to work closely with dogs, which had been a passion ever since her parents took her to a dog show when she was a child, hoping to get her involved in a sport or competitive activity. They lost track of her for a time, according to Viltz, only to find her in a large grooming cage with her arms wrapped around a massive Newfoundland.

While still living at home, she trained a miniature poodle named Tam Tam, unsettling her mother with marathon obedience tutorials that tested Ms. Killilea’s endurance.

“The superhuman patience, the physical struggle with what seemed to me to be insurmountable difficulties, were more than I could watch,” Marie Killilea wrote in 1983. “The session at an end, I would find Karen, her color high, drenched with perspiration. Her comment: ‘I don’t perspire — I sweat — most unladylike!’ ”

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