Entry in progress—B.P.
 
Wiktionary: fashionista
Etymology
Coined by Stephen Fried in Thing of Beauty: The Tragedy of the Supermodel Gia in 1993. It is a combination of fashion and the Italian, Spanish or Portuguese suffix: -ista. Compares to other -ista neologisms such as Sandinista, Peronista, Guardianista.
Noun
fashionista (plural fashionistas)
1. A person who creates or promotes high fashion, i.e. a fashion designer or fashion editor.
2. A person who dresses according to the trends of fashion, or one who closely follows those trends.
 
(Oxford English Dictionary)
fashionista, n.
A person employed in the creation or promotion of high fashion, as a designer, photographer, model, fashion writer, etc. Also: a devotee of the fashion industry; a wearer of high-fashion clothing.
1993 S. Fried Thing of Beauty v. 90   Many of the fashionistas were..runaways—people who had left their small towns for New York with no thoughts of coming back.
1996 Time Out N.Y. 4 Sept. 42/4   A universe of trendy promoters..ensures a crowd of beautiful people, suntanned fashionistas and their coattail riders, all air-kissing and cocktailing.
   
OCLC WorldCat record
Vague : Violet Pea, a fashionista: a girl with her own take on fashion
Author: R William Conway
Publisher: London : Most Beautiful House in the World, 1992.
Edition/Format:   Book : Fiction : English
 
The Atlantic
I Apologize for Inventing the Word ‘Fashionista’ 20 Years Ago
In 1993, an unsuspecting Gia Carangi biographer made up a word to collectively refer to the many tiny factions within the 1970s fashion industry. Today, it’s everywhere.
STEPHEN FRIED APR 17 2013, 8:46 AM ET
(...)
Since I was re-reading a lot of the newspapers and magazines from the period of Gia’s supernova career in the late ‘70s and early ‘80s, and remembering a lot of coverage of Sandanistas (and a lot of “–ista” jokes among my mag writer friends), I just decided to try it.

The word only appeared four times in the book, and it did not immediately catch on.
(...)
I never gave the word another thought, frankly, until it started showing up in the fall 1995 coverage of the European couture shows, both in the London Evening Standard and the Washington Post. A Lexis/Nexis search showed it was actually used three times in 1994, 26 times in 1995, 54 times in 1996 and 74 times in 1997.
   
Philly.com
Writer Stephen Fried apologizes for inventing the word ‘Fashionista’
POSTED: Thursday, April 18, 2013, 2:30 PM
What’s this? The person who invented the word “Fashionista” is from Philly?

Stephen Fried, the former editor-in-chief of Philly Mag, says he’s sorry for inventing the word “Fashionista.” In a recent Atlantic piece titled, “I Apologize for Inventing the Word ‘Fashionista’ 20 Years Ago,” the writer chronicles how he invented the word in 1993 when he penned a book titled, Thing of Beauty: The Tragedy of Supermodel Gia.
(...)
Fried writes that the word, which only appeared four times in Thing of Beauty, was not received favorably by several people, including his wife, linguista author Ben Yagoda, and New York Times book critic and fashion editor Carol Kramer. He writes that Kramer, “b-tch-slapped me for ‘fashionista,’ saying ‘he makes up corny labels, too.’”