Prepare, but do not bake, pie shell.
Combine rhubarb and water in saucepan, and cook over medium heat until rhubarb is tender.
Pour into blender or food processor, add strawberry drink mix, cornstarch and sugar replacement, and puree.
Refrigerate to chill completely.
Beat egg whites until stiff; beat rhubarb mixture to loosen.
Blend egg whites into rhubarb mixture and pour into pie shell, spreading evenly.
Attach a 2 inch (5 cm) collar of flour-dusted waxed paper.
Preheat oven to 400°F (200°C); reduce heat to 375°F (190°C).
Place pie in lower third of oven.
Bake for 30 or 35 minutes.
Insert wire cake tester in center; souffle is done if tester comes out clean. (Place waxed paper over collar to keep top from getting too brown.)