Kate Andersen Brower is a CNN contributor and the author of the new book " First in Line: Presidents, Vice Presidents and the Pursuit of Power. " She has written two other books about the White House, "First Women: The Grace and Power of America's Modern First Ladies" and "The Residence: Inside the Private World of the White House." Unless otherwise noted, facts in this piece reflect research from those works. The opinions expressed here are hers.

(CNN) Donald Trump and his eldest children were hunkered down with Washington lawyers at the President's golf club in Bedminster, New Jersey. It was the summer of 2016 and some combination of Donald Jr., Eric, Ivanka -- and Ivanka's husband, Jared Kushner -- had been meeting to help vet the vice-presidential candidates.

But at this final, decisive meeting it was Donald Trump's wife, Melania Trump, a former model seemingly disinterested in the political world her husband had flung her into, who drew the bottom line on a running mate.

Whoever is chosen must be "clean," she insisted.

That meant no affairs and no messy financial entanglements. It meant no drama and no Chris Christie and no Newt Gingrich. Her husband had a surplus of that already. It meant, ultimately, Mike Pence.

Now, more than 500 days into her tenure as first lady it is unclear whether Melania Trump still has the ability to persuade her husband in the White House, but she has certainly demonstrated that she does not intend to allow others to influence her decisions.

She did it just last week, when the President's personal lawyer, Rudy Giuliani, said Melania does not believe the allegations that her husband had an affair with porn star Stormy Daniels. "She believes her husband," Giuliani insisted. The first lady's communications director Stephanie Grisham fired off a shockingly candid tweet not long after and said: "I don't believe Mrs. Trump has ever discussed her thoughts on anything with Mr. Giuliani."

'No one speaks for me'

Melania Trump, as we by now have discerned, is a puzzle -- and with few friends who will talk openly and honestly about her. One of them, Paolo Zampolli, a modeling agent who discovered Melania and introduced her to Donald Trump, told me recently: "She's the first lady of the century. You have to go back to Jackie Kennedy to find anybody like her. Every day she is better and better." He could not cite any specifics but it seems clear, particularly from some of her early choices, that Kennedy is the first lady Melania seeks to model herself after.

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Zampolli, who still exchanges text messages with the first lady, said he suspects the world will be seeing more of her in the coming weeks, but he gave no indication of when or where. One would have to go back to Bess Truman to find a more private first lady.

When she disappeared from view for weeks after surgery to treat a benign kidney condition, she did not feel the need to reassure anyone that she was all right. Her absence triggered a flood of rumor mongering on the internet and a #WhereisMelania hashtag, but she did not emerge just because curious people wanted her to.

At one point last month when reporters asked the President, on the South Lawn, how his wife was doing, he pointed to the second floor of the White House, where the family's private living quarters are located, and said: "She's doing great. Right there. She's doing great. She's looking at us, right there." But reporters said there was no sign of the mysterious first lady peering down at them.

Melania is described by people who know her as "stubborn" and "unapologetic about who she is." Based on her past comments, Giuliani should have considered himself warned: "No one speaks for me," Melania once said when her husband promised a TV news anchor that she would appear on her show.

Melania Trump has redesigned the East Wing and the job description of what it means to be first lady in much the same way her husband has transformed the presidency: She has less than half the usual number of East Wing aides and she openly contradicts her husband's closest advisers, a no-no for any previous first lady.

When asked for examples of her influence on policy, Grisham told me in an e-mail, "The First Lady advises and gives her husband her opinion on many different topics."

She showed that she went her own way early on, refusing to move into the White House immediately, unlike all of her predecessors -- with the marked exception of Anna Harrison whose husband William Henry Harrison died a month after taking office.

And she waited more than a year to announce her signature issue. The "Be Best" campaign was finally launched last month, though we have not heard much about it since. On paper, the campaign seeks to take on cyberbullying and the impact of opioids on families.

One of her aides told me that she warned the first lady that there would be backlash to her taking on online bullying, especially since her husband is its most famous transgressor. In March, at a meeting with technology leaders Melania said she was aware of the criticism and simply did not care. "It will not stop me from doing what I know is right," she said.

Navigating the terrain between East and West Wing

Rarely we do see animosity between the East Wing, the domain of the first lady and her staff, and the West Wing made public, as we did with the Giuliani incident -- even though such tension has existed in every modern White House. Usually, first ladies quietly endure slights from their husband's top aides, as Pat Nixon famously did.

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Nixon adviser John Ehrlichman got a taste of this when he told Pat that he was worried that she had grown too thin. Ehrlichman said he was readying himself for tears or for anger, but her cold stare shook him to the core. This was how first ladies usually held their ground in the years before Twitter: by being stoic and silent. Like most first ladies, Pat was more liberal than her husband, she was pro-choice and she supported the Equal Rights Amendment. She unsuccessfully campaigned for him to nominate a woman to the Supreme Court for the first time.

The silence at the dinner table the evening of the announcement that he'd appointed two men was broken by an angry Pat. The President sighed heavily and said, "We tried to do the best we could."

Of course some first ladies have no problem inserting themselves in West Wing decision-making. Nancy Reagan thought her husband's chief of staff Don Regan was not up to the job and orchestrated his firing. He had hung up on her twice, which is something no one did to Nancy Reagan. "You might have been able to get away with it once, but not twice!" the Reagans' son, Ron, told me.

Hillary Clinton went so far as pushing to be her husband's domestic policy chief, but the President's pollster, Stan Greenberg, convinced her that it would be disastrously unpopular. Having a West Wing office was bad enough.

Michelle Obama speaks bluntly. She made it clear from the beginning that -- like Melania -- she did not appreciate other people speaking on her behalf. In Obama's case she resented her husband's aides making promises that she would show up at events without first consulting her. She wanted to be in control of her own schedule but she never went public about tension with the West Wing because, before Melania, it simply was not done.

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There are lessons for Giuliani here. He should be aware that Melania -- unlike first ladies before her -- could continue to make the life of a presidential adviser very difficult in the White House if she chooses to. And he should also know that this is a first lady who has proven that she will not follow protocol and keep family feuds quiet.