“Letters to Jackie” — the opening film of the AFI Docs film festival that starts Wednesday — is a somber revisitation of President John F. Kennedy’s assassination by way of letters written from a supportive populace to first lady Jacqueline Kennedy.

Based on the book “Letters to Jackie” by Ellen Fitzpatrick, the movie takes a sample of the book’s most compelling notes from a range of writers — from a sympathetic wife to a socially concerned postgraduate to a 13-year-old polio victim. The film employs 20 prominent actors, including Betty White, Viola Davis and Jessica Chastain, to recite them. The letters are read aloud as footage from the Kennedy era is projected.

More than 800,000 letters were written to Jacqueline Kennedy from around the world.

Janis Hirsch wrote one of the selected letters in January 1964, about two months after the president’s death. She was 13 and recuperating from a broken hip that was a result of polio.

“I was in the hospital in a full body cast, and after the cantor from our temple came by and told me [about the assassination], all I could do was watch the television and freak out quietly,” she says in a telephone interview.

The Kennedys were important to her family, Hirsch says: The only day her mother let her skip school was when John F. Kennedy visited Trenton, N.J.

Hirsch, now 62, came home from the hospital on the day of JFK’s funeral.

“I couldn’t go to any rallies or anything because I was stuck in bed, all so helpless, so I decided to write a letter to Jackie,” she says. “I wanted to try to help her.”

She recommended a song to the former first lady.

“I will tell you my remedy for some smiling and happiness. Always sing ‘You Gotta Have Heart’ from ‘Damn Yankees’ and I think you’ll be happy,” Hirsch wrote more than 49 years ago.

Hirsch, who now lives in Los Angeles and is a television writer, is one of a handful of letter writers who will be in Washington for the film’s opening. She is bracing to see her teenage mistakes in a much larger format (and read by Hailee Steinfeld) but is excited to be presented with this letter again.

“To be connected to your young self is a stunning gift,” she says. “We all have memories of what we were like as a kid, and it wasn’t like seeing your homework but it was really what you were feeling and who I was starting to be.”

And about that song?

“Oh yes, I still sing it,” she says. “It still works.”