You still have time to make your mother a lovely cake. HERE'S my recipe, but the site with the nut-free marzipan layer has gone kaput. Basically, it is softened butter kneaded with flavouring and enough confectioner's/icing sugar to hold together and roll out. You'll know when you have it right because it will no longer stick when you roll. Keeping it well chilled helps too.
The ball decorations are made from the same buttercream as the rolled layer, but set in the freezer on a plate to harden and then dipped in white chocolate. Keep them chilled until they set. Once the cake has been decorated, you should store it in the fridge, but an hour out on the table shouldn't do much harm this time of year, unless you live in a warm climate.