I did a Wilton cake course earlier this year, and the main thing is that it is all about the texture of the icing. Although in saying that, it was buttercream icing so it might not be the thing for your DD.
I made this cake for my DD's 3rd birthday:
A trick is to freeze the cake before you carve it into shape. If you are using bits of cake then glue them on with icing (I didn't and it fell apart when we cut it!!). you can cover the cake with icing then roll out fondant icing and lay it over the top. Use cornflour to roll it out in as icing sugar is too sticky.
If you just want a cake with a picture on top, then you can find a picture online (go for a simple one - like a colouring book picture) then trace it onto baking paper, go over the image with writing icing (clear or white) then lay it on the top of your already iced cake. Then you should have a copy of the picture on top of the cake, you can then fill it in with icing. Good luck!! Also remember even if it doesn't look perfect, it will taste delicious <span class="emoticon smile">smile</span>