1. Mist a 9-inch springform pan with cooking spray. Line sides of pan with ladyfingers, flat sides in; you will have 1 ladyfinger left over.
2. In a food processor, puree 1/2 of strawberries with 1/3 cup sugar. Pour 1/2 cup water into a small saucepan. Sprinkle with gelatin; let stand 3 minutes to soften. Place pan over lowest heat and cook, stirring, until gelatin dissolves, about 1 minute. Stir in remaining 1/3 cup sugar and cook, stirring, until sugar dissolves. Transfer to small glass measuring cup; let cool to room temperature.
3. Using an electric mixer on medium-high speed, beat cream until soft peaks form. Beating constantly, add gelatin mixture in a slow steady stream, beating just until stiff peaks form. Fold in berry puree and sliced berries. Transfer mixture to springform pan and smooth with spatula. Cover and refrigerate for at least 6 hours or overnight. Top with whipped cream and halved strawberries.