Carol Lynley obituary in “The New York Times” in 2019.

Carol Lynley a child model who went on to an intense film acting career mirroring the country’s transformation from the modest Eisenhower era into the sexually frank 1960s, died on Tuesday at her home in Los Angeles. She was 77.

The cause was a heart attack, according to Trent Dolan, a friend.

Ms. Lynley may be best remembered as the naïve, soft-spoken adolescent who becomes pregnant by her equally wide-eyed boyfriend, played by Brandon De Wilde, in the 1959 film “Blue Denim.” It was a role she had originated on Broadway the year before, when she was 16.

Ms. Lynley made at least half a dozen high-profile Hollywood movies over the next eight years, but by the time she was in her mid-20s her star had faded and she was never solidly in the public eye again.

Still, she did make a notable if brief comeback in 1972, when she turned up wearing hot pants and go-go boots in the disaster movie “The Poseidon Adventure,” singing (or at least lip-syncing) the Oscar-winning song “The Morning After.”

Her career may have been, at least partly, a victim of unfortunate marketing. In the late 1950s and early ’60s, Hollywood’s publicity machine had three blond teenage actresses to promote. In a case of extreme image segmentation, Sandra Dee was promoted as the pampered rich girl, Tuesday Weld as the bad girl and Ms. Lynley as the good girl — studious, sensitive, wholesome and just a bit prim.

This worked well enough with the characters she played in her debut film, the Disney drama “The Light in the Forest” (1958), set in pre-Revolutionary America; in “Blue Denim”; and in “Hound-Dog Man” (1959), in which she starred opposite the teenage idol Fabian. But beginning when she was 19, Ms. Lynley turned to portrayals of more knowing characters, like the small-town author Allison MacKenzie, who has an affair with her publisher, in “Return to Peyton Place” (1961), a disappointing sequel. That film was followed by a sex comedy, “Under the Yum Yum Tree” (1963), with Jack Lemmon and Dean Jones, and by the drama “The Cardinal” (1963), in which she played both Tom Tryon’s wayward sister and her character’s daughter.

She was 23 when she posed discreetly nude in Playboy magazine and played the title role in “Harlow” (1965), a biographical film about the 1930s screen star and sex symbol Jean Harlow. That same year, she won some positive reviews as a distraught young mother in Otto Preminger’s “Bunny Lake Is Missing,” but neither critics nor fans responded to her in the same way as they had during her teenage years.

From the 1970s onward, Ms. Lynley worked mostly in television, doing guest appearances on various shows (she was in the original television film “Fantasy Island” and in at least 10 episodes of the series that it spawned, as well as the television film that later became the Darren McGavin series “Kolchak: The Night Stalker”) and in low-profile movies, some of the straight-to-vid