Pour your rosé into large ice cube trays or a 9x13 pan. Freeze until almost solid, at least 6 hours. (it won't completely solidify due to the alcohol, so don't worry, you can easily pop them out of the ice cube trays or scrape it out of the pan)
When your rosé is just about ready, bring sugar and ½ cup water to a boil in a medium saucepan. Cook and stir constantly until sugar is dissolved, about 3 minutes. Add strawberries, remove from heat, and let the mixture sit for 30 minutes to infuse with strawberry flavor (I gave it a couple stirs to help).
Strain the syrup through a mesh strainer into a bowl (do not press on the strawberries...you don't want any solids going through the strainer). Cover and chill until cold, about 30 minutes.
Pop your rosé cubes (or scrape rosé from the pan) into a blender. Add lemon juice, 3 1/2 ounces of the strawberry syrup, and 1 cup of crushed ice. Blend until smooth. Transfer to a freezer safe container to thicken the frosé back up, at least 30 minutes.
When ready to serve, blend the mixture again until it is nice and slushy. Divide among 4 glasses and enjoy!