When we were in WDW a few years ago we ate HBD and I ordered the Grapefruit Cake (deeelish!) and the waiter gave me a copy of the recipe. I don't have that copy handy now but here is a recipe I found online in case you ever want to make it for your mom ..... or me.
Grapefruit Cake
The Hollywood Brown Derby at Disney Hollywood Studios
1-1/2 c. Sifted Cake Flour
3/4 c. Sugar
1-1/2 tsp. Baking Powder
1/2 tsp. Salt
1/4 c. Water
1/4 c. Vegetable Oil
3 Eggs (separated)
3 tbsp. Grapefruit Juice
Grated Lemon Rind
1/4 tsp. Cream of Tartar
Sift together flour, sugar, baking powder, and salt into a mixing bowl. Make a well in center of dry ingredients. Add water, oil, egg yolks, grapefruit juice, and lemon rind. Beat until smooth. Beat egg whites and cream of tartar separately, until whites are stiff but not dry. Gradually pour egg yolk mixture over whites, folding gently with a rubber spatula until just blended. Do not stir the mixture. Pour into an ungreased pan. Bake at 350 degrees for 25 to 30 minutes, or until cake springs back when lightly touched with a finger. Invert pan on cake rack until cool. Run spatula around edge of cake and carefully remove from pan. With a serrated knife, gently cut layer in half. Yield 4-6 portions.
Grapefruit Cream Cheese Frosting
2 6-oz. pkgs. of Cream Cheese
2 tsp. Lemon Juice
1 tsp. Grated Lemon Rind
3/4 c. Sifted Powdered Sugar
6-8 drops Yellow Food Coloring
1 one-pound can Grapefruit Sections
Let cream cheese soften at room temperature. Beat cheese until fluffy. Add lemon juice and rind. Gradually blend in sugar. Beat until well blended. Add food coloring. Crush several grapefruit sections to measure 2 teaspoons. Blend into frosting. Spread frosting on bottom half of cake. Top with several grapefruit sections. Cover with second layer of cake. Frost top and sides. Garnish with remaining grapefruit sections.