When Dr. Ruth Westheimer was first asked if she wanted to be the subject of a documentary, her answer was swift and decisive: Absolutely not. She was too busy, and besides, she’d talked plenty about her decades-long career as a renowned sex therapist. She simply wasn’t interested. At all. 

But then producer Rafael Marmor sent her a link to one of his prior films called “No Place on Earth.” Instantly, the title resonated with her. During the Holocaust, when she was just 10, she’d been separated from her parents in Germany and sent on a Kindertransport to an orphanage in Switzerland. Her family’s decision saved her life; they were all killed by the Nazis. But at the end of World War II, when she and the other surviving orphans were transported to Israel, that was how she felt — like there was nowhere in the world where she belonged.

“So a few days after sending her my documentary, I got a call from a 212 number that I didn’t recognize,” Marmor recalls. “And it was, like, ‘Hello? Rafi? I am very interested now. Let’s talk.’”

Westheimer enthusiastically agreed to participate in “Ask Dr. Ruth,” which premiered to glowing reviews at the Sundance Film Festival. The film, which will be released in theaters and on Hulu this spring, explores the diminutive doctor’s contribution to the sexual revolution through her offering of often humorous, always candid advice. (Westheimer received a doctorate in education from Columbia University in 1970.)

It is also a portrait of resilience, depicting how the 90-year-old — or, as she calls herself, a 90-and-a-half-year-old — immigrant triumphed over tragic circumstances with the aid of a positive attitude.

At Sundance, Westheimer went on a full-on charm offensive, telling everyone she could that she wanted the documentary to be nominated for an Academy Award next year. Bounding around the mountain town in her Merrells — “child’s size 4, I wear!” — she made friends everywhere she went, holding hands with reporters during interviews and befriending her driver (she got him a ticket to her documentary premiere, “plus a Hulu hat”).

“She gives everything such a positive spin,” says Marmor, who would grow so close with Westheimer that she invited herself to his wedding last year and told him she’d be speaking at it. “We’ll sit down at a restaurant and she’ll say, ‘This is amazing! Fantastic! Delicious!’ Every driver she has is the best driver, and she’ll tell the driver how fantastic the drive was.”

Westheimer traces her upbeat nature to her early childhood socialization. Before the Holocaust, she says her upbringing in an intact family home in Frankfurt was idyllic. Her grandmother was a religious Orthodox Jew who emphasized the importance of trusting in God, her father encouraged her to study hard and pursue education, and even in the toughest of circumstances — when she was saying what would be a final goodbye to her daughter at the railroad station — her mother told her, “We’ll see each other again.”

“For my master’s, I followed those children who came (like) me from Germany with similar backgrounds, with love, and they all made it,” Westheimer explains. “None of them committed suicide. None of them became a drug addict. None of them fell on the wayside. None of them had psychological problems that stopped them from being productive members of society.”

But while she is happy to share her joy with anyone she encounters, Westheimer refuses to let herself publicly express any sadness. In the documentary, her daughter, Miriam, notes that she has seen her mother cry only once: at her father’s deathbed.

“She just doesn’t allow herself that good, deep cry that you allow yourself when you need to get rid of pain,” Miriam, one of Westheimer’s two children, says in the film.

It’s just something that’s in her blood, Westheimer theorizes. She never saw her parents cry because “German Jews don’t show their emotions in public.” Privately, she says, she has grappled with anguish. In the ‘80s, when she wrote her autobiography, she visited a psychologist and opened up about the sadness she felt over leaving her parents.

“There was a time that I thought that if I stayed with them as a young child, I could have saved them,” she says. “Nonsense. If I had stayed, I would not be alive.”

While she allowed director Ryan White to follow her on her annual pilgrimages to Switzerland and Israel, she told the production she had no interest in visiting the concentration camp where her parents were sent. “I did not want to go to Auschwitz, because I’m not going to stand there and cry in front of other people,” she says.

“I often heard the line, ‘I’m the therapist, you’re not the therapist,’” remembers White, best known for his work on “The Case Against 8” and the Netflix docuseries “The Keepers.” “She doesn’t touch the trauma and pain she went through. For a sex and relationship therapist, I think she’s surprisingly not very emotional.”

While she delves into the sex lives of others, Westheimer also has clear boundaries when it comes to discussing her personal life. She was married three times but calls her last marriage, to fellow German Jew Manfred Westheimer, who died in 1997, her “real marriage.” She still wears the yellow diamond he gave her on her ring finger. “It’s beautiful. Everybody admires it,” she says, showing it off. “You can’t have it! You can try it on, but you can’t have it.”

She understands why people might assume she’s been promiscuous — this is a woman, after all, who advised all of her film producer’s wedding guests to “try a new position and report back!” at his rehearsal dinner.

“I let them believe that, but I’m rather old-fashioned and a square,” she admits. “If people think that somebody like me who talks about sex from morning till night is sleeping with somebody every night, they’re mistaken. Just going out and having sex might be fun, and if you’re protected against an unintended pregnancy or unintended sexual disease, it might be all right. But it is not satisfying.”

She says she’s heartened by the conversation that has emerged from the #MeToo movement, though she stresses the importance of therapy for those who allege they have been sexually abused. She is also unsure how the evolving discussion around consent will affect interpersonal relationships.

“It’s very difficult for me to say, ‘Come in with a piece of paper and make him or her sign that you’re willing to go to bed,’” she says. “I want people to look at each other. I want them to hold hands. I want them to have a glass of wine. I want them to talk about it. But there is no question that we have to teach the younger woman that they have to have a right to say ‘no’ and that we have to teach men that even though the desire to have sex is very open and strong, that they have to respect the other person.”