1. Make the simple syrup: In a small saucepan, bring the sugar, rosé, and rosewater to a boil. Simmer until the sugar water is dissolved, about 3 minutes. Remove from the heat and let cool completely. Store syrup in a glass jar and save for up to 1 month.
2. Combine all ingredients except for the peach in a large bowl. Use a liquid measuring cup to carefully fill popsicle molds about halfway with the mixture. Freeze until just set, about 1 hour.
3. Add a few cubes of peach to each mold (the set layer prevents the peach from sinking to the bottom) and add more of the rosé lemonade mixture—just enough to fill the molds about three-quarters of the way. Insert popsicle sticks and freeze until completely set, about 4 hours.
4. Run the molds under warm running water for a few seconds to loosen the popsicles, then remove and serve. Drink any leftovers or use to make ice cubes.