Pour rosé into a medium-size metal bowl, cover with plastic wrap, and freeze 4 hours or overnight. When ready to prepare cocktails, scrape frozen rosé with a fork to break up, and return to freezer while preparing other ingredients.
Process sorbet, elderflower liqueur, and simple syrup in a blender until smooth, 10 to 15 seconds. Add to rosé, and stir until well blended. Spoon into frozen or chilled glasses. Garnish, if desired, and serve immediately.