The day before you plan to make your frosé, add all the berries to a blender and puree. To remove the seeds, pour the mixture through a mesh sieve and discard seeds and solids. Pour the puree into ice cube trays, freezer-safe containers, or freezer bags. You'll need to put the puree into the blender once frozen, so you want to freeze it in small portions that will fit in the pitcher of your blender.
To make the simple syrup, combine water and sugar in a small saucepan over medium heat. Bring to a simmer and cook for 5 minutes or until sugar is completely dissolved. Remove from heat and cool completely before using.
To make the frosé, combine simple syrup, wine, and frozen berries in a blender. Blend on high speed until well blended and the mixture is nice and slushie.
Pour into glasses to serve! Store frosé in a freezer-safe container. Allow to thaw slightly before serving again. You can also put it back in a blender to freshen it up before serving again.