Clicking on the "find out more" shows that it's a heavy-ish layered sponge underneath. The decoration (as the company name suggests) is coloured white chocolate, either moulded (the big letters, hearts) or hand shaped for the flowers.
Have you phoned and asked how much?
There's a huge amount of work there.
Assuming your daughter is not actually after something over a metre high for 400 people, and you have a LOT of time on your hands, then you could:
Make a set of cakes of different sizes and stack them up (hire a set of tins from the cake shop). Sponge will probably be ok but cut the tops off so they stack square.
The cake shop will also be able to sell you some big sugar letters.
For the rest of the decorations use fondant moulding paste - make out of glucose and icing sugar - it's *much* easier to work with than chocolate.
To cover the cake before putting on the decorations, you can use more fondant icing - it's very easy to fix if you tear it or cock it up. Or you could use a white chocolate fudge iciing (or even callebaut coating-grade white chocolate if you can get it) which you can pour over from the top and it will flow down and set semi-hard.
The local library will probably have a shelf full of books on how to make flowers out of moulding paste.
Watered-down food colouring and modelling paintbrushes for the detail...
Simples!
