For her father’s recent retirement party, Marisa Noel Brown had the enviable task of choosing between two Angel Sanchez gowns, which the designer had delivered to her SoHo duplex the day before the event. The first was deep Chinese red, with a plunging neckline and a swishy train; the second was a purple column with an asymmetrical ruffled strap over the left shoulder. To go with the dress, she had a choice of several pairs of spangly, sky-high Roger Vivier shoes, and jewelry by a Mexican designer, Daniel Espinosa.

At first, Brown was sure she would wear the red dress—it seemed quintessentially Sanchez. The up-and-coming Venezuelan trained as an architect, and Brown likes the clean-lined simplicity of his designs. “His clothes all have an architectural feeling. They’re very bold,” she says. “It’s not so much about an intricate, lacey detail, but about bold colors that really stand out.”

After trying on both dresses and catwalking across her bedroom floor, Brown ultimately chose the violet gown. “The red one looked better on the hanger, but these dresses really come to life when you try them on,” she says. “The purple one was so striking. It just suited me best.”

Though it’s hard to imagine the dress that wouldn’t suit Brown’s tall, lithe frame, she has an expert’s discerning eye for what looks good on her and what doesn’t. After all, she grew up in a family accustomed to black-tie events and is a fixture on the New York City social circuit. She goes to several dozen formal parties a year and is photographed frequently, so she can’t repeat any outfits.

Fortunately, Brown doesn’t have to buy a dress for every occasion. Like many of the highest-profile members of New York’s smart set, she borrows clothes from fashion houses that are all too willing to have their garments appear in magazines on wealthy and well-connected young women. “I’m very lucky that once you start getting photographed, designers come to you,” says Brown.

These days, she works almost exclusively with Sanchez, who became a good friend when she asked him to design her wedding dress in 2002. “It’s a running joke with us that I’ll show up the day before an event and say, ‘I’m going to the New York City Ballet—I need some help,’” says Brown. “And he always says, ‘Oh, Mar, why didn’t you give me some warning? I could have done this or that for you.’ But I know there will be something fantastic at his showroom that I’ll love.”

Brown, who has two young sons with her husband, Matthew Brown, a managing director of her father’s hedge fund, says she has scaled back considerably on her social schedule in recent years. “When I was 24, I probably went to five parties a night. But you can’t keep doing that forever. You can’t go to everything because then you would have no cozy dinners at home or with your friends.”

So she accepts invitations to benefits for organizations she truly cares about, namely the nonprofit organization New Yorkers for Children; Endeavor, which supports entrepreneurs from emerging economies; and the Museum of the City of New York, which her husband’s great-great-grandfather founded. But as any veteran fund-raiser knows, if your friends come to your benefits, then you have to go to theirs. Her calendar fills up quickly.

Brown has been called a socialite, but it isn’t a moniker she’s particularly fond of. “It connotes ladies who lunch and don’t do a lot else,” she says. “And that doesn’t really describe me and it doesn’t describe any of my friends. We’re all busy and we work or have children.”

She says she hopes her ties to these organizations do some good. “I volunteer for New Yorkers for Children, and it’s very close to my heart,” she says. “And even if it’s not an organization that I volunteer for, the reason I’m going to a benefit is because they’ve told me that it helps their organization to buy a ticket and tell my friends to go.”

And, she admits, it’s a lot of fun. “They’re always such beautiful parties with delicious food and wonderful people. You feel so glam and cool getting dressed up in New York City, especially when you’re wearing Angel Sanchez. And I walk out onto my cobblestone street and hail a cab and off I go.”