After A Show, NYC, September 2015.
A simple way to wear a very summery dress during cooler weather: add a turtleneck (or a skivvy as we call them in Aus!). 
Recreate her look (kind of):
White turtleneck — Vince Favorite turtleneck, Splendid Supima cotton turtleneck top, ASOS The turtleneck,  Alix Varick Turtleneck bodysuit, M.Patmos turtleneck sweater, Selected Femme women's turtleneck jumper or Three Dots turtleneck
Simple slip dress — J Brand Maryanne Slip Dress, T by Alexander Wang silk-georgette dress, Raey Deep V-silk slip dress, ASOS Mini Cami slip dress in rib, MM6 Maison Margiela cotton-jersey and satin-jersey dress, Topshop Cross Strap slip dress, ASOS Cami slip dress, The Row Gibbons crepe midi dress, or Jacquemus Pleated linen-paneled wool dress