I have a customer who would rather have fresh flowers placed on her cake rather than gumpaste flowers. The cake will be covered in fondant. How do I make sure that the flowers stay fresh prior to delivery throughout the night.

You get the florist to deliver them very early on the day you deliver the cake, if at all possible. Otherwise, you get the florist to give you instructions on how to keep them fresh, although fresh-cut flowers should last more than a couple of days. I'm harping on the florist, because getting flowers for a cake from a florist is the only safe way to make sure they're free of pesticides and other contaminants. And make sure you put them in those little food-safe plastic thingies (I forget what they're called) before you stick them in the cake: you should never stick plant stems directly into the cake.