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But despite the financial windfall that her success has brought her -- she recently purchased and is in the process of renovating a Bel Air mansion and was able to pay off her mom's mortgage and buy her uncle his "dream boat" -- Sweeney is acutely aware that her fame and income could disappear with "one wrong move."
In a recent profile in Glamour, the "Anyone But You" star said her experience not having money growing up has influenced how she approaches her wealth.
"I come from a family where I saw my parents lose everything, and I am terrified of that," she said. "That fear will always be instilled in me. I'm a huge saver. I don't just go and spend money. I like to invest. I like real estate. I like making, hopefully, smart choices with the money I'm making. But I don't think I'll ever actually feel comfortable."
Sweeney's family moved from rural north Idaho to Los Angeles when she was 13 so that she could pursue acting, a decision that she previously told the Hollywood Reporter placed the family under severe financial strain and ultimately led to her parents' divorce.
Though she's now known for her love of cars, she was stuck driving her "grandparents' old Volvo" when she first started driving in LA.
"I had to jump-start it to get it to go. The bottom casing fell off while I was driving," she told Glamour. "Oil would spill everywhere, so I always had cardboard to put under the car so it didn't stain anybody's driveway."
While the days of driving a beater are long gone, Sweeney said has a hard time coming to terms with her success.
"It's a weird feeling when people are like, 'Oh, you're successful,' or say, 'You've made it,'" Sweeney says. "It doesn't feel like that because there's so much more I want to accomplish and achieve. I feel like I've barely scratched the surface of what I'd like to do in my life."
And though she might never feel comfortable financially, she's proud of how far she's come.
"I'm a very successful, independent woman who's worked really hard," she said. "I've accomplished and bought everything myself, and I provide for myself and my family."