Forget long years of anonymous apprenticeship in the shadow of a Donna Karan or Marc Jacobs—still the norm in Paris and Milan. Today’s designers come to New York with the expectation of more immediate, personal success. And they are getting it.

The other day, Ms. Fetherston, a striking blonde with blunt-cut bangs, was seated on a fluffy white couch in the old studio, wearing a massive, chunky black vintage sweater and a pair of slim navy blue jeans from her Target line. “They’re pretty good!” she said. “What I’m really excited for is just to see the clothes on people in the street. I think that’s when I’m going to really kind of flip out.”

Until now, Ms. Fetherston’s light, ethereal fashions have been critically acclaimed, but hardly recognizable on everywoman—and perhaps that is part of their appeal. “I think she’s very talented,” said Sally Singer, the formidable fashion features director of Vogue, who has championed Ms. Fetherston ever since the latter lived in Paris, where she attended design school at the Parsons School of Design’s sister campus. “She’s part of a generation of quite talented and singular designers, in the sense that they have quite unique visions and they stick to them regardless of where trends are going.”

During the most recent Fashion Week, Ms. Fetherston seemed to be everywhere—at Glamour’s party for the charity Malaria No More, for which she designed a T-shirt; at British publisher Jefferson Hack’s party at the Bowery Hotel—in sky-high heels and short dresses (always) of her own design, practically levitating. She stands 5-foot-10 and has excellent posture, and like the models in her shows, she often wears creative white headgear. The color of her hair blends with the color of her skin, all of it glittery and translucent. “You always know where she is in the room,” said Sarah Easley, co-owner of Kirna Zabête in SoHo, the first Manhattan retailer to sell Ms. Fetherston’s clothes. “She’s like a living fairy.”

Ms. Easley said that the draw of a Fetherston collection is not its timeliness but its timelessness. “It’s not 2008 particularly, or 15 years ago, or 15 years forward,” she said. “You can’t really place it. It’s sort of floating above. She really operates in a vacuum of what Erin likes. Kind of like how the most stylish people just dress for themselves—it’s like Erin designing for Erin. And we like Erin.”

A FRILL A MINUTE

Ms. Fetherston was born and raised in the Bay Area; she refused to say what her parents do for a living. She moved to Paris after graduating from Berkeley in 2002 with a degree in interdisciplinary studies. It was there that she met her fiancé, Hedi Ferjani, 32, an artist, with whom she recently began cohabiting in Tribeca (they will keep a pied-à-terre in Paris), at a brunch in someone’s apartment. “It was a total, as they say in French, coup de foudre—lightning strikes, love at first sight,” she said.

Likewise, the designer completed her studies in a brisk two years. “I just wanted to get in, absorb, and get going,” she said. “I casually thought, ‘I’m going to start making the clothes I’ve always dreamt of making, and we’ll see what happens. I was working with lace, cutting pieces out, hand-painting them; I really went nuts.”

With just one seamstress, Ms. Fetherston assembled a collection of 33 “looks” to show during the January 2005 Couture Week in Paris (albeit off-calendar; only eight houses are officially sanctioned as couture). This, she said, helped her escape a common Catch-22 facing young designers: “To be bought, you need to have some press. And to get some press, you need to be selling somewhere.” In couture, a designer’s retail viability is less a concern than “my vision, my aesthetic, and my name,” as Ms. Fetherston put it, and soon enough, American Elle had tracked down her phone number. “I didn’t totally pre-calculate it,” she said. “But it all sort of worked out.”

Next came ready-to-wear. “I was like, ‘Let’s really get those clothes out there in the world.’” Ms. Fetherston said. It helped that she had befriended fashion photographer Ellen von Unwerth, as well as the actress Kirsten Dunst, who was filming Marie Antoinette at the time. “I just sort of met her, no big story,” the designer shrugged.

The three women decided to make a short film based on the collection. “We just wanted to create something beautiful,” Ms. Fetherston said. “And it was sooooo fun.”

Their movie, Wendybird, features a jubilant Ms. Dunst and several pretty young models frolicking around a lake full of birds, wearing frilly dresses they find hidden in a chest under a tree. Shot in black and white, set to slow versions of “Summertime” and “You Showed Me,” it portrays a rapturous, otherworldly idea of femininity in which frills constitute a kind of freedom. “They’re supposed to be clones,” Ms. Fetherston said of the characters. “And when they find these clothes, it kind of breaks the spell on them.”

For the Target collection, she and Mr. Ferjani collaborated on another short, Dollhouse, in which two girls on bicycles discover a doll house in the woods and shrink to its proportions; dress-up again ensues, this time more campy and set to music reminiscent of The Nutcracker. There’s also a tea party.

Ms. Fetherston’s first Bryant Park show, for spring 2007, was accompanied by another collaboration with Ms. von Unwerth—a series of photos themed “Urban Flowers.”

“I was walking in New York, feeling really deprived of nature,” the designer said. “I’m from California, and even in Paris we have a lot of parks, and I was feeling like I had not seen a living green thing. And literally on Canal Street, it was so dirty, and I saw this little daisy growing out of a crack in the sidewalk, and I was like, ‘You’re so lovely and wonderful!’ I just saw it as being a great metaphor for who I kind of think the Erin Fetherston girl is. Because she really takes you by surprise, and might not necessarily belong, but is really beautiful and uncontrived, sort of thriving in a tough environment. I got together a whole band of girls who I thought embodied that idea.”

The photos, shot by Ms. von Unwerth in Williamsburg, feature the actress Zooey Deschanel, artist Sarah Sophie Flicker, model Karen Elson, designer Catherine Holstein, the Traina sisters (Danielle Steel’s daughters) and Ms. Fetherston herself, smiling against backdrops of weedy, graffitied decay.

Next came a collaboration with Ms. Deschanel, who opened Ms. Fetherston’s fall 2007 Bryant Park show with a solo performance of “Dream a Little Dream.” “She has this great jazz voice,” Ms. Fetherston said.

Despite her glamorous chums, Ms. Fetherston has mixed feelings about using famous people to promote her clothes. “The values of my collection—a sense of whimsy, a sense of romance, girly-cute style—there are a handful of celebrities who to me totally embody that, and I adore them,” she said. “It’s really exciting to see the dress go on the right kind of personality.” But “it’s almost like celebrity is currency. It’s kind of a rough business.”

Ms. Fetherston’s most recent Bryant Park show, her third, attracted an impressive numbers of socialites, editors and celebrities, including Lauren Davis, actress Brittany Snow, It models Irina Lazareanu and Agyness Deyn, Ms. Deschanel and Anna Wintour, who arrived early and was photographed alone in the front row, waiting patiently.

The collection was an assortment of white and gray dresses and trousers, soft and monochromatic and worn by models with bleached eyelashes and softly feathered hair. Many wore white turbans (“I can’t imagine not finishing an outfit with a headpiece,” said Ms. Fetherston). She even sent her first pantsuit down the runway—soft, flowing and white, but a pantsuit nonetheless. “I’d never really thought of her as someone who does trousers,” remarked Ms. Singer.

Back in her studio, Ms. Fetherston played the Target commercial, which debuted Monday during MTV’s The Hills—a three-minute short film that features a girl getting dumped by her boyfriend and then attending a big soiree. “Whether you’re planning the party or having your own pity party,” Ms. Fetherston says in a voice-over. “What you’re wearing is important.”

It’s a distinctly un-Fetherston statement—a jolt of modern marketing reality into her dreamy aesthetic. “I think that there is a great element of escapism to my whole universe,” Ms. Fetherston admitted. “I was a little unsure about the commercial concept at first. It was a little too real for me, the girl getting broken up with; I was like, ‘Yuck, yuck, yuck!’ But I came around, because I think the message was, these things do happen. They happen to me all the time. But the clothes can help to transport you to that state of mind.”

She had donned a white turban from her spring 2008 collection—“very Grey Gardens”—with a subtle bird head protruding from its front, like some sort of antique feminine spelunking light.

“People say, ‘Are you ready to be a household name?’” Ms. Fetherston said. “And I guess we’ll have to see if that’s going to be the case.”