Combine 2 cups water and sugar in a medium saucepan; cook over low heat, stirring constantly, until sugar dissolves. Cook over high heat, without stirring, until mixture reaches soft ball stage (240°).
Soften gelatin in remaining water. Add to syrup mixture, stirring until gelatin dissolves. Cool to room temperature. Stir in 1 cup orange sections and juice. Chill to consistency of unbeaten egg whites.
Beat whipping cream and marshmallows until soft peaks form. Fold in pecans. Fold marshmallow mixture into orange mixture.
Line bottom and sides of a 9- inch Springform pan with split ladyfingers. Spoon orange mixture into prepared pan. Cover and refrigerate overnight.
Remove sides of pan; place charlotte on a serving platter. Sprinkle top with coconut; garnish with remaining orange sections and orange slices.
Note: One (6 1/4-ounce) package miniature marshmallows is equivalent to 1/2 pound large marshmallows, chopped.