After a summer spent visiting Thailand, Cambodia and Laos with her sister plus a family trip to Sardinia, Margherita Maccapani Missoni is heading to New York on official fashion family business.

The 26-year-old Missoni brand ambassador and model is heading to New York (she recently sold her apartment and stays at the Bowery Hotel) to play hostess at her family’s Madison Avenue boutique for tomorrow night’s worldwide fashion party. Missoni’s mother (and the brand’s designer), Angela, will be helming festivities at the label’s Milan boutique.

“There are so many cool events that night,” she told The Post via BlackBerry last week while she was in LA. “I hope to stop by Bergdorf Goodman to support Missoni and my friends Zac Posen and Ashley and Mary-Kate.”

Famous friends are just the beginning of it. At the cocktail party tomorrow night, Missoni will be joined by Rachel Zoe. The two will offer shoppers styling tips and advice on how to personalize the store’s exclusive FNO totes. The limited-edition bags — in green, pink and black and white — will retail for $60, and proceeds benefit the National September 11th Memorial and Museum.

Missoni says she’ll be in town only until Monday, and she plans to catch Posen’s runway show as well as attend both Vanity Fair’s and Saks’ Fashion Week events. And she’ll be eating at both of them, thank you very much.

“It’s impossible to be on a diet during Fashion Week,” she says. “There are too many dinners and cocktails. My only suggestion is to drink as much water as you can!”

Recently the Italian heiress said she’s made a few key fall purchases — namely Azzedine Alaia calfskin booties, Golden Goose latex leggings and Missoni’s lace jogging pants — with a tight friends-and-family discount, no doubt. But she says to ask Mama for this season’s must-haves: the brand’s hoodies and long scarves, of course!