I would do the box of cake mix with two round pans like others have suggested. Also, I use boxed mix and I do this to it to make it taste better: look at the directions on what to use and use an extra egg, double the oil amount BUT use melted butter instead of oil, and use milk instead of water. It makes the cake taste so much better and not as oily!
As for the decorations...I would skip the fondant and try to use it during the year for next year. It is easy to make a cake look nice with just icing. I'd find a basic icing tip and bag kit and make some homemade icing. Here is my mom's recipe that I have used and everyone loves it:
2 boxes of confectioner's sugar
1 cup Crisco
2/3 cup warm milk
1 tsp vanilla
Mix salt, vanilla, and crisco together. Add sugar a little at a time until mixed in. Then add warm milk (NOT HOT). You can't overbeat it.
i would do a box cake mix - it will be easier for you and less stressful. i usually use vanilla or chocolate canned frosting for the filling. to also save time you can buy a bucket of wilton buttercream frosting at wal-mart for $13, you can also get it at michaels or i-party. what is her theme? sometimes if my schedule is very busy and the kids want their cake decorated a certain way and i might not have time or be able to do it, I will have mt local supermarket print out a picture of my childs choosing onto edible paper. just put the pic on the cake and add some edging around it so you don't see the seam. easy! if you are around a shaws or stop and shop (and some super walmarts) they will print out pictures for you for about $7. Big Y no longer does it, they will only print a pic for if you buy one of their cakes.