There are a lot of things I make that are low fat. Frosting is not one of them.
Favorite Frosting for the Holidays

8 oz Cream Cheese (You could use reduced fat cream cheese)
8 oz Unsalted Butter
4 cups powdered sugar
2 tsp vanilla

1. Beat with electric mixer: cream cheese and butter.

2. Beat in sugar and vanilla.

3. Add food coloring and yum!