In a large bowl, whip the cream with the vanilla extract until stiff peaks form. Dollop large spoonfuls onto a parchment paper lined baking sheet and freeze until firm, about 3 hours. Once frozen, peel the whipped cream from the paper and place in a large blender. Add the strawberries, lemon juice, and 2 tablespoons of the sweetener. Blend until smooth. Add the ice and water and blend until well combined. Taste and add more sweetener if desired. Pour into 4 glasses and serve.