Combine the sugar and water in the small pot and bring to a boil. Reduce heat to a simmer and continue to cook until all of the sugar is dissolved, about 5 minutes. Reserve ½ cup of the syrup and transfer the rest to a bowl to cool completely. Store in a plastic squeeze bottle in the refrigerator.
Cook the Rhubarb
Stir the thinly sliced rhubarb with the simple syrup and bring to a boil. Reduce heat to a simmer and cook, covered, until the rhubarb is very tender, about 5 minutes. Remove from heat and allow to cool to room temperature. You can make this one day ahead and store in the refrigerator.
Mix the Sherbet
Process/blend the cooked rhubarb and syrup with the strawberries and lactose-free lowfat milk until smooth.
Freeze in your ice cream maker according to the manufacturers directions. Transfer to a plastic freezer container and freeze for about 2 hours before serving. Sherbet may need to sit at room temperature for 5 minutes before serving if it’s hard.