Prepare the fondant flowers and allow them to set.
Prepare the fondant unicorn horn and let it set.
Once the cakes have cooled down, level and sandwich the cake layers with buttercream.
Cover each of the 2 tiers with white fondant and stack them together. Use bubble straws for support.
Cover the cake board with white fondant.
Attached the fondant unicorn eyes on the side of top tier with shortening.
Wrap the sides of the cake board with purple ribbon. Secure it in place with some hot glue.
Using the same colored satin ribbon, wrap it around the border of each cake tier. Secure it to the cake with some royal icing.
Attached the prepared fondant unicorn horn on the top tier.
Next is the fondant flower mane. To guide the placement of the flowers, roll a long thin strip of fondant and attach it to the sides of the cake, in the way you wish to place the flowers.
Start attaching the flowers from the top tier, right at the horn. The first color is red, followed by orange, yellow, green, blue, pink and purple. And then repeat the colors in the reverse order, such that the last color at the bottom of the second cake tier is red. Attach the flowers with shortening.
Next, make and attached the unicorn ears on the top tier of the cake with some fondant glue.
Finish decorating the unicorn's floral mane by filling up the gaps in the mane with smaller fondant flowers.
For the birthday girl's name, mix CMC powder into some white fondant. Knead it well and roll and cut out the letters for the birthday girl's name.
Paint the front of each fondant letter with edible gold paint. Let the paint set.
Finally, attach the fondant letters to the cake board with fondant glue to complete the decoration for the unicorn birthday cake.