Set aside 4 strawberries for garnish.
In 2-quart mixing bowl, using fork, crush remaining berries; stir in yogurt, orange juice, and sugar substitute.
In another bowl, using electric mixer on high speed, beat egg whites until soft peaks form; add sugar and extract and continue beating until stiff but not dry.
Fold beaten whites into strawberry mixture; transfer mixture to 2 freezer trays or a shallow baking pan, cover, and freeze until almost firm, about 45 minutes.
Chill mixing bowl.
Turn berry yogurt into chilled bowl and, using electric mixer on high speed, beat until thick and creamy.
Cover with plastic wrap and freeze until just firm.
To serve, let yogurt mixture soften slightly, just until it can be easily spooned out; spoon into 4 ice cream or dessert dishes and garnish each with a reserved berry.