I made her a rainbow cake that I have seen several versions of on the Internet. I created mine using two white cake box mixes, the butter cake recipe from the Cake Mix Doctor, and some gel food dye. I used each box mix to make three layers of the cake. I thought it was a good plan, but I ended up with a cake that was very tall.
I made a double batch of the butter cream frosting recipe also from the Cake Doctor cookbook and used very little between the layers and had just enough to frost the sides. And assortment of rainbow colored sprinkles were use to decorate the top.
The cake was enjoyed by all, especially the birthday girl.