Leslie, who was also a novelist and playwright, died Feb. 2 of pneumonia at her Beverly Hills home, said her daughter, Diane Leslie.
“A Date With Judy” was originally conceived as a radio vehicle for her friend, actress Helen Mack, whose "crazy stage mother" kept pestering Leslie to write a show for Mack, Diane Leslie said.
By the time the teen-angst comedy debuted on the radio in 1941, Mack was too old to star, but she directed episodes that Leslie wrote and produced.
During its radio run, which lasted until 1950, "A Date With Judy" was also made into a movie starring a teenage Elizabeth Taylor. Time magazine marveled that the "little lollipop of a cinemusical" made it to No. 1 at the box office in 1948.
"Date" was transformed again in 1951, this time into a daytime TV series that segued onto ABC's prime time schedule, airing live in 1952 and 1953.
In 1938, Leslie joined what is now the Writers Guild of America and was its oldest living member. For six months in 1956, she was the group's vice president.
She was born Aleen Wetstein on Feb. 5, 1908, in Pittsburgh to a traveling salesman and his dressmaker wife.
At Ohio State University, Leslie studied playwriting, but she left after three years, unable to afford to finish college during the Depression.
Soon after becoming a secretary for the influential Assn. Against the Prohibition Amendment, she started writing a weekly column, “One Girl Chorus,” for the Pittsburgh Press in 1933. She kept up the column for nearly a decade.
With press pass in hand, Leslie gained entrance to Columbia Pictures and eventually talked her way into a writing job in the late 1930s. She started out on short "Three Stooges" films.
She was one of about two dozen female screenwriters at the time, according to her daughter, and had compiled 19 film credits by the late 1950s.
They included "The Doctor Takes a Wife" (1940) with Ray Milland and Loretta Young and "Father Was a Fullback" (1949) starring Fred MacMurray.
Her ease in writing for teenage characters came into play when she worked on several 1940s Henry Aldrich movies, which were Paramount's response to MGM's Andy Hardy series.
In 1939, she married Jacques Leslie, a Pittsburgh attorney who became a prominent entertainment lawyer.
The couple were self-absorbed and career-driven, going through dozens of nannies at their Beverly Hills mansion, their daughter said.
In 1999, Diane Leslie wrote a fictionalized but comic account of her "typical Hollywood childhood." At the center of the bestselling "Fleur de Leigh's Life of Crime" was a self-involved actor-writer based on her mother.
When Diane offered to excise anything her mother objected to, Aleen responded, "Object? I'm the star of the novel," and showed up at book signings, pen in hand.
"My mother had a great sense of humor," Diane said last week. "She was darling. . . . I really did love her."
Aleen's second child, Jacques, also became a writer. In 1972, he was a Times foreign correspondent when he was wounded covering the war in Vietnam.
Leslie penned two novels, "The Scent of the Roses" (1963) and "The Windfall" (1970), and wrote a number of plays. One, "Slightly Married," had a brief run on Broadway in 1943.
She was a "two-desserts-a-day person" who smoked for 50 years, quitting only after her husband died at 65 in 1974, her daughter said.
At a gathering last summer, a great-grandson accidentally hit a baseball straight toward her. With the tenacity that marked much of her life, the frail 101-year-old reached out and caught it.
Besides her two children, Leslie is survived by her brother, Robert Wetstein, 96; three grandchildren; and three great-grandchildren.