The Godolphin-owned filly had shown her liking for the Normandy track with a victory at the top level in the Prix Saint-Alary and made a triumphant return to France with a smooth performance.
James Doyle had the Charlie Appleby-trained filly in a good position just off the pace set by Body Sculpt and Vue Fantastique.
Sobetsu quickened nicely into the lead and, after seeing off French Oaks scorer Senga, kept final challenger Onthemoonagain at bay.
Appleby said: "We ran her in the Oaks and she didn't stay a mile and a half and then she ran very well in the Nassau.
"She's got plenty of options in the autumn so we'll probably give her a bit of a break and either come back to Chantilly on Arc weekend or look at the Queen Elizabeth at Keeneland."