"I'm not anti-plastic surgery at all," the 46-year-old tells U.K.'s Good Housekeeping for its March cover story, which hits newsstands Tuesday.
As she promotes the movie version of the British sitcom Dad's Army, the Welsh actress says "you don't have to be a beauty queen to be an actress," and adds the roles she is now being offered are different and "more interesting."
But, she says, "Contrary to public opinion, I have not been under the knife ... yet, is what I say!"
"If I feel like it, I'm going to go ahead and do it! If [surgery] makes you feel better, who am I to tell someone that it's wrong?"
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"You've got to keep the home fires burning!" she says. "It's a long road and I think people today are so quick to throw in the towel on marriage.
"You have to give it your best shot and not give up when the first problem arises, because that won't be the last problem. There will be many more down the road."
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The couple have had their very public bumps, including a short separation in 2013 as they battled the stress of Douglas' cancer struggle and her bipolar disorder.
But they celebrated their marriage in November 2015 with a dinner date coupled with a message of love on Zeta-Jones' Instagram. "Happy Anniversary dearest Michael! Loving our life together, here's to the next 15!" she wrote.
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She tells the magazine the celebration "was great. Just the two of us at one of our favourite restaurants, laughing that we haven't killed each other yet – and that we are still alive! Fifteen years is a long time."
She also reveals that she has learned to manage her illness better, even though she describes it as a "pain in the ass!"
She adds, "There are amazing highs and very low lows. My goal is to be consistently in the middle. I'm in a very good place right now. A lot of that is to do with the fact that I'm much more knowledgeable about [it]."