For the rhubarb sauce: In a small saucepan, combine the rhubarb, water and strawberry jam. Bring to a simmer over medium heat. Reduce heat to medium-low. Cover and simmer, stirring occasionally, until rhubarb is a sauce-like consistency, about 10 minutes. Set aside to cool.
For the vanilla mousse: In a mixing bowl, with an electric mixer on medium-high speed, beat together the coconut cream, vanilla extract, 4oz yogurt, and xylitol to semi-firm peaks. Reserve ¼ cup mousse for topping.
To assemble: Set out two martini glasses or wineglasses. Spoon ¼ cup mousse in the bottom of each glass and spread evenly. Top each with 1½ tbsp rhubarb sauce. Divide the remaining mousse between the glasses, then top with the remaining rhubarb. Top with the reserved ¼ cup mousse, dividing evenly.