To the OP, I would make copies of all receipts, all water, trash, electric, gas bills, all gas receipts from that week of working on the cake and delivering, and any copies of bilss, receipts otherwise necessary when making a cake. I would also use Excel to create a 'timesheet' of the hours you worked and include a total amount at the bottom of said timesheet (this alone should be about $400.) Then present all information to the bride just to let her know exactly what kind of deal she got.
But then, I'm a smarta$$ like that!
What she said!