Heat and stir gelatine and 1/2 cup water together until gelatine is melted.
Remove from heat and stir in the remaining water and the frozen lemonade.
Whisk in the ice cream and chill in the freezer until mixture begins to set, stirring occasionally, about 10 minutes.
Scrape into the prepared pie shell.
Chill until set, about 20 minutes.
Garnish with a whiff of whipped cream.