I've just asked SWM^H^H^HAmy this question, her response was simply that the moment you give over the copies, it stops being your concern. If she wanted things tweaking, she'd have asked at the time. If, 6 months later, she changes mind but your house has burnt down, it's her luck out. Likewise if she'd lost the files it would be her fault. The only time this wouldn't be the case is if she'd paid you money specifically to keep them.