In a large kettle, cook rhubarb and water over medium-high heat for 3-5 minutes or until rhubarb is tender. Add sugar. Bring to a boil; boil for 2 minutes. Stir in pie filling, blueberries and lemon juice. Return to a boil. Reduce heat; cook and stir for 10 minutes. Remove from heat; stir in gelatin until dissolved. Cool slightly. Pour into refrigerator containers. Cool to room temperature. Cover and refrigerate.
If using frozen rhubarb, measure rhubarb while still frozen, then thaw completely. Drain in a colander, but do not press liquid out.