what a pity! but well every disaster is a learning experience, i had my fondant melting the other day on an engament cake! i was able to quickly remove and replace just before delivery but i learnt a lesson which i think you can also learn - ice cakes at least 2 days to event! That gives the grace of 1 day in case there is need to correct any errors or pending disasters.Meanwhile for sake of maintaining good human relationships you can apologise and refund her money.