I think he easiest way would be to buy a small amount of fondant , color portions of it the correct colors with gel type food colors (all these things are widely available at Michaels, JoAnns, etc.) roll out each color, and cut out the shapes and put them together like a puzzle, or even layered on top of each other. Its a fairly simple figure. Cut out the shapes with a sharp knife or exacto knife (on a surface you can cut on of course - I cut through an expensive silpat mat once
). then just lay it on top of your cake. you can lay it on top of fondant or buttercream. Good luck. She will appreciate the effort.