Since Versace was the sponsor of the party, Donatella Versace outfitted the actresses Lindsay Lohan, Taylor Momsen and Mischa Barton in her designs. “They tried to get me to wear their stuff, but it seemed too kiss-ass to wear the sponsor clothes,” Ms. Macklowe told The Observer, adding: “Last season I feel like it was all long ball gowns, and this season I think I will be in all short. It just feels more appropriate, you know?”

Ms. Macklowe, 31, is married to Billy Macklowe, son of real estate developer Harry Macklowe. She has a small, fit frame; blond, shoulder-length hair; and squinty eyes. She speaks loudly and laughs a lot. She does not care about society-appropriate etiquette and generally avoids the straight, evening-appropriate gowns worn that same evening by Debbie Bancroft, Lisa Anastos and Laurie Tisch, from whom she holds herself somewhat apart. In her own words: “If you’re of the socialite set, you have to care. They are somewhat limited to what their fashion sense is, and is it even theirs? I don’t care. I do what I want.”

Born in Aspen and raised in Arizona, Ms. Macklowe, nee Lerner, graduated from the University of Virginia (’99) in three years with three majors: finance, economics and information management. After a few years in private equity and “doing LBOs” (leveraged buyouts), she moved to New York to work for Metropolitan Capital and was set up on a blind date with Mr. Macklowe. She said she was not familiar with his last name.

“Billy says I was very shy and bashful,” said Ms. Macklowe, chatting with The Observer at the Whitney Studio Party, later on. “He’s probably the only person who has ever thought I was shy or bashful!” They married in 2004 at the Metropolitan Club and had a daughter, Zoe, in 2007.

UNTIL THE END of last year, Ms. Macklowe was a portfolio manager for Sigma Capital Management, one of Steven Cohen’s funds, but after the economy fell apart, she was laid off. Macklowe Asset Management (JMACK Capital), born in January, is a seed fund of Millennium Partners, Israel (“Izzy”) Englander’s fund, and is housed at 666 Fifth Avenue. There, Ms. Macklowe manages some $250 million in investments.

“People were shocked that we were launching a fund when the world was coming to an end,” she said. “But it’s very typical of me. Everyone goes one direction, I go the other.”

Fellow socialite-financier Alexandra Lebenthal told The Observer: “While $250 million seems like an enormous amount of money, to a hedge fund it’s nothing. They spend that on lunch. Successful hedge funds are measured in billions of dollars, so $250 million is just not considered that significant. But bear in mind, it’s seed capital, so if she does well, Millennium could add more money and then other people will add more money.”

Ms. Lebenthal also praised Ms. Macklowe’s initiative. “The hedge fund world is a man’s world,” she said. “It is testosterone-laden, and successful women are very few and far between and that is not because they lack the talent.”

Ms. Macklowe is not particularly popular with other benefit-attending wives who (anonymously) whisper that she’s “too loud,” too “out there,” too “strange.” Which—along with the fact that she always buys, never borrows—is exactly what has made her the darling of the fashion set.

“You see all these amazing things on the runway, and very few people have the guts to wear them,” Ms. Macklowe said. “Anyone can wear something that’s safe, but you have to have a certain amount of courage to … like one year I wore a Zac Posen dress to the CFDAs. It was all one piece of yarn in little pieces and I actually hit the worst-dressed list somewhere!”

Among the other things she’s worn: head-to-patent-leather-toe Chanel (tweed suit, thigh-high white boots) to the Juicy Couture store opening last year; the notorious sculpted Balenciaga floral dress to the 2008 Metropolitan Opera premiere gala; the voluminous hot-pink spatter-painted Dolce & Gabbana dress paired with fingerless leather gloves to the Costume Institute gala last year; a pant-less Lady Gaga look with the Rodarte blazer and Chanel combat boots to a New Yorkers for Children gala in April; and a purple and pink Jason Wu ruffled minidress to the opera just last month. Mr. Wu’s dress is the only of these she borrowed, since it had appeared on the runway in his spring 2010 show just a week prior and was not available for purchase.

“SHE REALLY OPERATES her closet like a business,” said Robert Burke, her good friend and the former men’s fashion director of Bergdorf Goodman. “She looks ahead and plans ahead and the way that she approached buying clothes is very strategically done.”

“She’s a sincere risk taker who doesn’t make her bold, unexpected choices simply and cheaply to turn heads, but chooses more from an almost unspoiled girlish glee in clothes,” said his colleague, Bergdorf women’s fashion director Linda Fargo. “Have you seen her full-wattage smile when she’s really decked? Someone should really bottle and brand her. Forget Barbie! Can you imagine buying Julie dolls and playing her video fashion games with that closet, imaginary places to go and business deals to seal?”

Ms. Macklowe stressed that her current shopping habit is an earned pleasure. Before she made her own money, she said, “I was very fashionable, but I was shopping at Contempo Casuals and Wet Seal and Charlotte Russe. You always have the appreciation, but you can’t always afford that stuff when you’re 21 unless you’re of a family that’s giving you money, which mine wasn’t!” (Ms. Macklowe’s father works in residential real estate in Arizona; her mother is a housewife.)

Julie’s husband, Bill ( who after famously bad-mouthing his own father in a Wall Street Journal article, took over leadership of the much-diminished Macklowe family empire in 2008), does not enjoy going to benefits as much and, according to his wife, is “amused” by her fashion choices. “For our fifth anniversary he has banned all benefits,” Ms. Macklowe told The Observer at the Whitney. Mr. Burke is often her date to various social functions.

“I’ve been to their house a number of times for dinner,” he said of the Macklowes. “They really complement one another. They both have a lot of energy. They have definite opinions. They are both very quick and witty.”

And who wears the pants? “Oh, I wouldn’t even get near that one!” he replied. 

On this particular evening at the Whitney, Ms. Macklowe was accompanied by her friend Jen Failla, whom she introduced as a “hedge fund chick, too.”

When asked if she ever raids her friend’s wardrobe, Ms. Failla, who was wearing a more conventional Dolce & Gabbana gown, said, “Well, I could maybe wear her tops, but not her bottoms. They’re a little Shakira.” (Shakira was, in fact, also a guest that evening.)

The Observer told Ms. Macklowe that given the invitation, we would gladly borrow a few pieces. “Well, you’re little more badass,” Ms. Macklowe said.

“Hey, I’m badass, too!” Ms. Failla piped up, seemingly not wanting to come off prudish.

“Well, she has an image to portray,” Ms. Macklowe said. “I don’t.”

ialeksander@observer.com