so she needs to make it for 16 but the recipe is for 4 so you need to do 16/4=4 so with that knowledge you need to times every ingredient in the list for 4 by 4 to get your answer for the recipe for 16:
100gx4=400g plain flour
2x4=8 eggs
300mlx4=1200ml milk
50gx4=200g cocoa powder
hope it helps!!