It only makes sense that such an unprecedented president-elect should have an unprecedented First Daughter. And to Donald Trump, Ivanka has long been first among equals.

Of his five children, she is peerless. During a family interview with Barbara Walters last year, Eric, Donald Jr. and Tiffany Trump all said Ivanka, 35, is their father’s favorite. When asked, years ago, how he ranked Ivanka and his other daughter Tiffany, Trump said there was no contest.

“Come on!” he said. “Daddy’s little girl!”

While the media has, as it should, assiduously reported on every official Cabinet appointment made by President-elect Trump, they have yet to vet the next administration’s most significant, powerful player: Ivanka. She’s not the first woman to sub for a first lady — most notably, Teddy Roosevelt’s daughter Alice did — but none had the influence Ivanka likely will.

Forget adviser: Ivanka, now moving her family to DC, may be co-president.

“The only phone call Donald would always take,” a Trump insider told Politico last July, “was Ivanka.”

Last week, Trump’s team floated Ivanka as inhabitant of the First Lady’s office in the East Wing. Ivanka also began personally lobbying Congress on child-care legislation.

Even if Trump’s wife, Melania, hadn’t announced that she’d be staying behind in New York City to see their 10-year-old son, Barron, through the end of the school year, the campaign itself proved that Ivanka’s opinions and advice, her branding and image, were prized most highly by Donald.

It was she, not Melania, who introduced the candidate at the Republican National Convention. In her speech, Ivanka sanded down the image of her father as a grotesquerie who rates women on a scale of 1 to 10, who has traded in wife after wife for younger, hotter models, who once boasted that Ivanka herself was so hot that, if not for biology, he’d be dating her.

“At my father’s company, there are more female than male executives,” Ivanka said. “Women are paid equally for the work that we do and when a woman becomes a mother, she is supported, not shut out.”

She spoke of the wage gap, of the difficulty working mothers have in getting the raises and promotions working fathers do, of the need for affordable child care. Her sleight of hand was a microcosm of the campaign’s: Here was the 35-year-old daughter of a billionaire, wife of a multimillionaire developer, glossy and groomed and convincing a huge swath of the electorate that she understood their struggles.

Yet what does Ivanka Trump really believe? In the course of a normal campaign, a candidate’s spouse comes in for public examination. They make speeches, give interviews, do the ritual “60 Minutes” appearances — because, as the unspoken truth goes, no one has more proximity to a sitting president, let alone power, than the First Spouse.

We get to know, to an extent, who this person is. We have yet to get answers from Ivanka.

Maybe we don’t want them yet. At this moment, she’s not just an enigma — she’s a national Rorschach test.

For those terrified of a Trump presidency, there is some solace in Ivanka, the urban sophisticate who will surely keep her father on the rails. For Trump supporters, she’s an aspirational avatar, proof that they’re not the knuckle-dragging hicks the media claims.

Ivanka’s very existence as Donald Trump’s favorite child is an exercise in cognitive dissonance.

Ivanka can be whatever the electorate wants: She’s registered as neither a Republican nor Democrat, identifying as an independent. She was raised Presbyterian but converted to Orthodox Judaism for her husband. Her mother, Ivana, is a Czech immigrant. Ivanka was raised in immense privilege yet never had the public missteps of peer Paris Hilton. She’s a businesswoman who devotes much of her social media to her kids. She seems very much a feminist, even though her dad has said sexist, misogynistic things.

Ivanka’s very existence as Donald Trump’s favorite child is an exercise in cognitive dissonance.

In the days after the election, Facebook COO Sheryl Sandberg, best-selling author of “Lean In,” reached out to Ivanka, as did Anne-Marie Slaughter, who worked as an adviser to Hillary Clinton. “She . . . can be a strong inside force,” Slaughter reportedly said.

It’s an optimistic statement. No one really knows where Ivanka Trump stands on abortion, Medicare, Social Security or ObamaCare, let alone the Middle East, Iran or North Korea. And if Ivanka’s weighing in on Kim Jong-un seems hyperbolic, remember: Trump met with Kanye West last week.

Perhaps Ivanka, like her father, is, more than anything, pro-money. For her RNC speech, Ivanka wore a dress from her own collection, retailing at $139. It promptly sold out. Her self-help book, “Women Who Work: Rewriting the Rules for Success,” will be published in March. And after the family’s post-election sit-down on “60 Minutes,” she hawked the $10,800 bracelet she’d worn from her own jewelry line.

The resulting public outrage seemed to catch her off guard. But in that interview, held in her father’s gilded Trump Tower apartment high above Fifth Avenue, Ivanka seemed secure in her new role and in the faith she believes voters have placed . . . in her.

There she sat on a small sofa, her father opposite, Melania in the middle. Asked how she felt on election night, Ivanka’s answer — more than any other utterance thus far — shows exactly where she sees herself: shoulder-to-shoulder with President-elect Trump.

“We’re very grateful for the opportunity,” Ivanka said. “And we take that opportunity very seriously.”