Geisel was a Chicago native and former nursing student at Indiana University.
She and Theodor Geisel, who was 17 years older, were both married to other people when they began an affair in the 1960s. His first wife, Helen, killed herself.
Audrey Geisel sent the two daughters she had with her first husband to boarding school after the Geisels married in 1968. The couple had no children together Seuss was not particularly fond of kids, she said.
He was afraid of children to a degree, Audrey Geisel told AP.
Geisel said she understood the gravity of what she was undertaking when her husband died, but said she was surprised how much work it was to oversee the business and philanthropy of the Dr. Seuss Foundation.
She tooled around tony La Jolla in a Cadillac with a license plate that read: GRINCH. And she showed up at events that celebrated her late husband.
In 2002, Geisel helped unveil bronze sculptures of Seuss and some of his most beloved characters at The Seuss Memorial in his hometown of Springfield, Massachusetts. The works were created by her daughter, Lark Grey Dimond-Cates.
When Audrey Geisel unveiled the sculpture of her late husband seated at his desk, her light blue eyes brimmed with tears as she bent down and kissed it.
Despite any anxiety her husband may have had around children, she wanted kids to crawl on the sturdy works.
"I'd like certain parts of it to get real shiny," she said, "because they have been rubbed so many times by little grubby hands."
In addition to being Seuss' protector and promoter, she also influenced his work.
When Seuss was writing the book that became "The Lorax," he got writer's block and she suggested they take a trip to get unstuck, Nel said. They traveled to Kenya, where workers cutting down acacia trees sparked an idea.
"He thought, 'They can't cut down my Dr. Seuss trees' which he renamed truffula trees and invented the Lorax to protect them," Nel said.
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Associated Press National Writer Hillel Italie in New York contributed to this report.