Step 1
Pour rosé into a 13×9″ pan and freeze until almost solid (it won’t completely solidify due to the alcohol), at least 6 hours.
Step 2
Meanwhile, bring sugar and ½ cup water to a boil in a medium saucepan; cook, stirring constantly, until sugar dissolves, about 3 minutes. Add strawberries, remove from heat, and let sit 30 minutes to infuse syrup with strawberry flavor. Strain through a fine-mesh sieve into a small bowl (do not press on solids); cover and chill until cold, about 30 minutes.
Step 3
Scrape rosé into a blender. Add lemon juice, 3½ ounces strawberry syrup, and 1 cup crushed ice and purée until smooth. Transfer blender jar to freezer and freeze until frosé is thickened (aim for milkshake consistency), 25–35 minutes.
Step 4
Blend again until frosé is slushy. Divide among glasses.
Step 5
Do Ahead: Rosé can be frozen 1 week ahead.
