cream cheese icing with white chocolate? google it, agree mascarpone with coconut. Or white chocolate granche however it wont be pure white. You can use glitter and sparkles to give it that wow finish.
I have done royal icing on chocolate sponge as I wanted it to be pure white. Worked well but used powdered egg white not fresh. It didn't set hard but stayed quite squishy. Not sure if that was the powdered egg white as I didn't but much glycine in.
I'd do royal icing, it should be ok on a sponge I reckon and you could sprinkle glitter or coconut on the peaks. My mum always did our christmas cake with lovely peaks to look like snow. I pop some glycerin in so it's not rock hard, which would make it easier to cut and hopefully stop the sponge cake breaking up! Maybe apricot jam on first to give it something to stick to?
Cooked American frosting, it isn't white white, because it has butter in it, but it's off white/cream and it's delicious. Google the recipe but basically you heat flour and milk in a pan like you're making a sauce until it's thick, then cool it completely until it's absolutely cold, and put it in a mixer with butter and granulated sugar and vanilla essence. It sounds like it should be horrid, gritty, floury, and it isn't at all, it's like dream topping off trifles, like sweet cream. It doesn't keep terribly well so you need to make it as near to when you want to use it as possible. It will make soft peaks like softly whipped cream. Perfect for a sponge cake. hth
What about royal icing? Icing sugar, water, egg whites. It's sets hard but you can use a fork to make it fluffy/peaky looking before it sets. .. You might need a layer of marzipan between it and the sponge though?
She actually likes all icing except fondant, she ate far too many black fondant penguins from last years cake and made herself ill (party food and excitement helped), so she now insists she doesn't like fondant.
I'm liking the coconut and glitter idea.
I wondered about covering it in buttercream but I thought that might not travel well, although I could encourage her friends to have a piece of cake for pudding rather than taking it home.
If she doesn't like fondant, I assume she won't like any kind of sugary icing? You could use 250g mascapone, a couple of tablespoons of icinging sugar just to sweeten it a bit, and about 50g of coconut mixed together, spread that over the cake (it's thick so try to sort of encourage it rather than spread it) and then sprinkle with more coconut to make it 'snowy'. You could sprinkle over some edible glitter too to make it christmassy.
How would you cover a sponge cake to look like a snow scene?
DD wants a club penguin cake but doesn't like fondant, I'll either be making some club penguin figures out of fondant (which can be taken off her piece) or I'll be buying a ready made topper, dependant on time.