Dissolve rice flour in water in a bowl and pour into a saucepan over medium heat. Whisk milk, cream, and cornstarch in a bowl and pour into the saucepan. Bring rice flour and milk mixture to a boil. Add sugar and rose water; reduce heat to low and simmer, stirring constantly, until sugar is dissolved and pudding thickens, about 5 minutes.
Scoop pudding into small serving bowls and garnish with pistachios, almonds, and rose petals. Place bowls in the refrigerator to cool completely, about 1 hour.