Add chopped rhubarb and water to a large stock pot. Bring the mixture to a boil over medium heat. Reduce the heat slightly and simmer for 15 to 20 minutes until the rhubarb becomes very soft and starts to break apart.

Place a fine mesh strainer over a large bowl or pot. Carefully pour the cooked rhubarb mixture through the strainer to separate the liquid from the pulp. Let the liquid drain completely and gently press the pulp with a spoon to remove extra juice. Discard the pulp.

While the rhubarb liquid is still warm, stir in the granulated sugar. Continue stirring until the sugar fully dissolves and the mixture looks smooth.

Add the frozen pink lemonade concentrate, frozen lemonade concentrate, pineapple juice, and orange juice. Stir thoroughly until the frozen concentrates completely dissolve into the liquid.

Pour the prepared slush mixture into freezer-safe containers, leaving a little space at the top for expansion during freezing.

Cover the containers tightly and freeze for at least 8 hours or overnight until the mixture becomes firm and slushy.

Remove the frozen slush mixture from the freezer a few minutes before serving if needed. Use a fork or spoon to scrape and loosen the icy texture.

Fill serving glasses halfway with the frozen rhubarb slush mixture. Slowly pour chilled lemon-lime soda over the top and stir gently to combine.

Serve immediately while cold, bubbly, and refreshing.