Charmian Carr, an actress who had a single but indelible role in the movies as Liesl, the von Trapp daughter who was “16 going on 17” in the Rodgers and Hammerstein musical “The Sound of Music,” died Sept. 17 at a private care facility in Woodland Hills, California. She was 73.

The cause was complications from a rare form of dementia, said her daughter Emily Watkins.

Carr was 21 when she was cast in the 1965 film that would sweep the Academy Awards – and immortalize her as a spirited teen who prances around a gazebo with her beau and adoringly harmonizes to “Edelweiss” with her father.

Although she was the daughter of a vaudevillian actress and a bandleader, Carr had no previous acting experience and little musical training outside the church choir. She did, however, have a lovely voice, elegant elocution and glistening blue eyes.

Perhaps most importantly, she did not look her age – a principal selling point when a mutual acquaintance introduced her to Robert Wise, director of “The Sound of Music,” who by Carr’s account had already rejected would-be Liesls including Mia Farrow and Patty Duke.

Carr joined a cast headlined by Christopher Plummer as Georg von Trapp, a retired Austrian navy captain and widowed father of seven, and Julie Andrews as Maria, the rebellious Catholic novice dispatched to their Salzburg manse as a governess on the eve of World War II.

Based loosely on a true story, the original musical and film adaptation endeared the von Trapps to generations. Of the children, Liesl, the eldest, is the one audiences come to know best.

Carr’s biggest number was “I Am Sixteen Going on Seventeen,” a playful duet with her boyfriend Rolf (Daniel Truhitte), who protectively assures her that he is “17 going on 18.” After leaping with Liesl around a gazebo, where they have taken shelter from the rain, Rolf steals a kiss and flees – leaving Liesl behind to let out an exuberant “Wheeee!”

Filming the scene, Carr skilfully concealed the pain from a sprained ankle: The wardrobe department had forgotten to put antiskid backing on her demure heels, and during one take of the dance she slid through the gazebo’s glass window.

The scene was one of several in which Carr was caught in the rain or drenched by a fall into a river during a jaunt with Maria. She acquired a certain allure, especially as “The Sound of Music” aged and audience singalong screenings invited parody.

“I guess it turned on a lot of teenage boys,” Carr once told the Vancouver Sun. “I never thought of Liesl as a sex symbol, but she was!”

After the success of “The Sound of Music,” Carr had a chance to appear on “Peyton Place,” but studio officials, fearful that the TV soap opera would sully Liesl’s persona, forbade her to accept.

Her only other significant role was in “Evening Primrose” (1966), a TV film with music by Stephen Sondheim in which she played a young woman living in a department store.

“It was hard to have your first role as the high spot of your career,” she once told the London Daily Telegraph. “I felt smothered by Liesl. She began to feel like my evil twin, the perfect one that everyone loved.”

Her acting career ended, she told the Calgary Herald, when she married a man who “didn’t want an actress for a wife.” She later appeared in commercials and became an interior designer. Her clients included Michael Jackson, who she said had a fixation on “The Sound of Music.”

Charmian Anne Farnon – her first name was pronounced SHAR-mee-an – was born in Chicago on Dec. 27, 1942, and grew up in California’s San Fernando Valley.

In “The Sound of Music,” she told an Australian interviewer, “music brought the family together – but in my real life music has torn my family apart.” Her parents were separated, and she recalled her mother, an alcoholic, remarking that “Charmian hasn’t got any talent. She’s just lucky.”

Carr was attending college, modeling and working in a doctor’s office when she met Wise, who suggested that she change her surname to the shorter Carr. She did her own singing in “The Sound of Music,” although a sister, Darleen, was among the singers who provided high notes for the actors.

Carr’s marriage to Jay Brent ended in divorce. Survivors include two daughters, Jennifer Svensson of Hermosa Beach, California, and Emily Watkins of San Diego; two sisters; a half-brother; a stepbrother; and four grandchildren.

Carr said that in time she came to accept her identification with Liesl. She hosted “Sound of Music” singalongs, wrote a memoir, “Forever Liesl” (2000) and released a book, “Letters to Liesl” (2001), both with co-author Jean Strauss, about missives sent to her by the movie’s fans.

“When people look at me and see Liesl, I believe they are looking into a mirror,” she wrote in her memoir.

“If the film has touched them in some way, it is because it represents the world as they want it to be. If it makes them feel love or happiness or hope, it is because they have these feelings inside them.”