Inventories are being kept tight in hope of increasing full-price selling and reducing markdowns.
The music star had launched the collection last February during New York Fashion Week.
The French designer was synonymous with striped sweaters and Left Bank insouciance.
The exhibition tracing the career of the fashion maverick is to arrive in Paris in April 2015.
She succeeds Marie Lannelongue, who has headed the magazine since its launch in France in 2004.
Guests including Tom Ford, Sarah Burton, Mario Testino and Amanda Wakeley crowded into The Wolseley on London’s Piccadilly on Thursday.