Rinse 1/4 cup dried hibiscus flowers in a fine mesh strainer under cold, running water. Set aside.
Bring 1/2 cup water to a boil in a small saucepan. Add 1/4 cup sugar and stir until dissolved. Stir in the rinsed hibiscus flowers. Remove from heat and let the flowers steep until slightly cooled, about 15-20 minutes. Strain through a fine mesh strainer.
Pour 1 bottle rosé wine into a large, flat container, like a 9x13" baking pan or large food storage container (it's helpful if it has a well sealing lid). Stir in the hibiscus syrup. Cover with the lid, or with plastic and freeze until flaky, at least 6 hours. Scrape into a blender and blend until slushy. Serve immediately, or pour into an insulated thermos or water bottle to keep cold.
Notes
Dried hibiscus flowers are available in the Latin section of a well stocked grocery store, or in a Latin market. Alternatively, you can make a berry version. Simply follow the recipe above, but use 1/2 cup of raspberries or chopped strawberries in place of the hibiscus.If you have a favorite rosé, go ahead and use it. You don't need to use an expensive wine here, since you'll be sweetening it up anyway. I used a medium priced one from Aldi and it worked out great.