There were moments in Bella Thorne’s life when the former Disney Channel star believed in the supernatural. Like the time when she was around 9, and saw an old woman crossing the road, then disappearing. Thorne thought, “No way, no way that that was fake!”

And then there was the time, after her family moved into a house on that same road, her sister’s date refused to pick her up because a “creepy-ass old woman” was in the yard.

“He never heard that [first] story before,” Thorne tells The Post. “So why would he make [up] an older woman? It was just weird. Weird vibes.”

Those vibes are part of what drew her to her new supernatural thriller, “I Still See You.”

In the movie, in theaters and on demand Friday, a lab experiment goes wrong, killing millions of people; 10 years later, their ghosts haunt the Midwest. These “remnants” are considered harmless — until one starts to stalk a teenager named Roni (Thorne), who embarks on a terrifying journey to discover why she’s being targeted.

Thorne, who turned 21 on Monday — an event she celebrated with KFC, Champagne and a flight to Las Vegas with her besties — has had a busy month. “I Still See You” is her fourth film to arrive in the past three weeks, following the dark comedy “Assassination Nation,” the thriller “Ride” and the Lifetime flick “Conrad & Michelle: If Words Could Kill.”

Being busy, it seems, suits her.

“I can’t not work for maybe two to three days in a row,” she says. “My mind gets weird with me if I’m not working constantly.”

A native of Pembroke Pines, Fla., just outside Miami, Thorne was born to Tamara and Delancey Reinaldo Thorne. After her father died in a motorcycle accident when Bella was 9, the family — including Bella’s three older siblings, Dani, Kaili and Remy — lived off food stamps.

But Thorne got her big break in 2010, at age 13, on the Disney series “Shake It Up” opposite Zendaya. Thorne played the sassy dancer CeCe Jones, and she sang on each of the show’s three soundtrack albums. Since then, she’s hardly ever stopped working, on TV (Freeform’s “Famous in Love,” MTV’s “Scream”) and in movies (the teen comedy “The DUFF,” Tyler Perry’s “Boo! A Madea Halloween” and the romance “Midnight Sun” with Patrick Schwarzenegger). She also heads a record label, Filthy Fangs, and has two rap-heavy albums of her own coming soon. She’s even written a book trilogy, beginning with “Autumn Falls,” whose red-haired, dyslexic teenage heroine reads much like Thorne’s own history.

“There’s a tremendous authenticity to Bella,” says director Scott Speer, who reteamed with Thorne for “I Still See You” following “Midnight Sun” and plans to work with her again. “I think the reason she really resonates with people is, what you see is kind of what you get.”

And you get a lot — Thorne’s 18.2 million Instagram followers know her for her work as much as the provocative choices she makes behind the scenes. Her distinctly wild sense of style and evolving hair colors keep the blogs busy, as do her raunchy rap lyrics (her most recent single is titled “P - - - y Mine”), skin-baring social media posts and atypical romantic life.

Thorne, who came out as bisexual in 2016, confirms that she’s dating two people at once: She calls the rapper Mod Sun her boyfriend and the YouTuber Tana Mongeau her girlfriend. But she stops short of using the label “polyamorous.”

“It’s definitely really intriguing and quite beautiful that you can open yourself up to have this kind of fluid relationship between three or four or five or however many people,” she says. “But I just don’t know that we like names or roles … We just kind of love each other. I don’t know that I could put a word on it like ‘polyamory’ because polyamory has its rules and its specifications, and I don’t know that I would specify these two relationships under any certain box.

“But just know that it’s awesome,” she adds, laughing. “I really am living the best of both worlds.”

Recently, Thorne addressed much of the criticism thrown her way through an ad campaign for Diesel’s Hate Couture collection. In the promo, Thorne sports a crop-top that reads “Slut.”

“I’m so sick and tired of everyone being their cleanest selves, and it’s like everything is so bubble gum,” she says. “God forbid you say the word ‘whore’ or ‘c–t’; you must be like the devil … Like, oh my goodness, people, calm down.

“Wearing a shirt that says ‘Slut’ right across it … it’s kind of a weird balance. You wear it and you feel better, yet then you also are constantly reminded of what people say of you or think of you,” she says. “It’s an interesting mind f–k and mainly why I wanted to do it … I’m Bella Thorne; I f–king love a good mind f–k.”