WASHINGTON — As anyone associated with the Trump administration knows, it only takes one outburst — a few haphazard emojis here, a call to The New Yorker there — to cement a new reputation. This week, in the time it took her to type out an Instagram screed, Louise Linton transformed herself from the Treasury secretary’s wife to a Real Housewife of the Treasury.

The protests and rallies and arguments roiling the country for months have not seemed to bother Ms. Linton, a Scottish actress who spent the summer after her wedding to Steven Mnuchin posting evidence of her lavish lifestyle on Instagram.

She zipped around on a speedboat in an Italian lake. She sipped wine at a restaurant overlooking the Louvre. She lounged in a very nice-looking pool with a very nice-looking giant inflatable swan, a tiny Chihuahua nestled in her arms.

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Along the way, Ms. Linton tagged and touted a parade of designers. “#TomFord.” “#Valentinorockstudheels.” “#HermesScarf.”

This in-the-clouds lifestyle abruptly collided with her husband’s political day job on Monday after Ms. Linton, 36, dressed down a stranger on Instagram for criticizing her travels. She apologized hours later, but it was too late to stop the social-media dredging of her past mistakes, including “In Congo’s Shadow,” a much-criticized memoir about her spotty gap year spent in Africa.

It was too late to stop critics from defacing her Wikipedia page, usually the first sign of any true social media frenzy. And it was too late to go back to her relatively under-the-radar Washington life. She even managed to upstage President Trump, a man who had just stared directly into the sun.

The debacle started after Ms. Linton took a day trip to Kentucky with Mr. Mnuchin and the Senate majority leader, Mitch McConnell. Ms. Linton, a spun-sugar blond who cuts an over-the-top glamorous figure in Washington, posted an Instagram photo of herself, Hermes bag on one arm and a Hermes scarf on the other, disembarking from a government jet. Her message contained praise for Kentucky: “#nicest #people #beautiful,” she wrote in Trumpian, hash-tagged prose.

As happens on social media, a stranger rained on Ms. Linton’s photo op by posting a mean comment.

“Glad we could pay for your little getaway. #deplorable,” Jenni Miller, a 45-year-old mother of three who lives in Oregon, wrote under the photograph.

Ms. Linton’s response was not quite as rose-colored as her original photo caption had been.

“Have you given more to the economy than me and my husband? Either as an individual earner in taxes OR in self sacrifice to your country?” Ms. Linton wrote.

She wasn’t done.

“I’m pretty sure we paid more taxes toward our day ‘trip’ than you did. Pretty sure the amount we sacrifice per year is a lot more than you’d be willing to sacrifice if the choice was yours.”

And then, Ms. Linton, fresh from a European vacation punctuated by rides at SoulCycle and trips to the Hamptons, delivered a blow to the offending commoner: “You’re adorably out of touch.”

Ms. Miller, the mother from Oregon, offered a similar criticism to The Times on Monday night.

“If she hadn’t made her account private, I would have written back with a very snide Marie Antoinette joke,” Ms. Miller said.

Ms. Linton is not the first woman associated with Mr. Trump to earn a comparison to Marie Antoinette. As protests erupted around the country over her father’s proposed travel ban in January, an Instagram photo of Ivanka Trump wearing a silver dress was quickly dubbed the “let them eat cake” photograph. Ms. Linton also is not the only woman in the president’s orbit who is dripping in diamonds and draped in Chanel.

But she is the first to be bluntly unapologetic about her luxurious lifestyle, one that affords her a comfortable, swan-shaped perch to view the country’s infighting.

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The other difference, of course, is that Ms. Linton is not a White House official, nor an elected one. She is an actress whose most recent work includes a role as a character named Betty on a 2016 movie called “Rules Don’t Apply.” She often shares photos of her past roles on Instagram. In July, she shared an image of a 2007 “CSI: NY” appearance. Her character in that episode was dressed as Marie Antoinette.

Ms. Linton, who declined to comment on her Instagram posts or her book on Tuesday, said in June that she met her husband at a wedding reception in Los Angeles in 2013. Since then, their Hollywood marriage — his third, her second — has had a rocky transition to Washington. During his confirmation process, Mr. Mnuchin was scrutinized for failing to disclose the full scope of his financial assets.

In May, after Mr. Mnuchin named Ms. Linton the interim chief executive of Dune Entertainment, a financing company he helped found, she stepped down after Democrats raised ethical questions, CNN reported. Ms. Linton said the position was meant to be temporary.

When in Washington, Ms. Linton said that she and Mr. Mnuchin, formerly of Goldman Sachs and a former Hollywood film financier, enjoy exploring the city. “DC Architecture reminds me of the architecture in Edinburgh where I was raised,” she wrote in an email in June.

The pair are often spotted dining at Cafe Milano or the Trump International Hotel, where in late July they had dinner with the president. Ms. Linton has readily found her place in a circle of distinctly Washington socialites, including Amy Baier, the wife of Bret Baier, the Fox News host, and Abeer Al Otaiba, the wife of Yousef al-Otaiba, the United Arab Emirates ambassador.

But the scrutiny over their lifestyle follows them. Even on day trips.

A Treasury Department official said that the Mnuchins had, in fact, reimbursed the government for the Kentucky trip. And Ms. Linton’s label-loving shout-out was not rewarded with free products or compensation, at least not in the case of her “#valentinorockstudheels” and “#valentino” tags, a spokeswoman for the brand said in an email on Tuesday.

Hours later, Ms. Linton did something rare for someone associated with Trump administration: She said she was sorry.

“I apologize for my post on social media yesterday as well as my response,” Ms. Linton said in a statement relayed through her publicist. “It was inappropriate and highly insensitive.”