I'm just finishing off some work for a client. She's been a nightmare and it's cost me far more to do the work for her than she's paying me, because of her constant changes of mind and endless e-mails to me, calls in the middle of the night etc. She is critical of my work even when I've way over-delivered. I've had enough, and want rid - and I've got a lot of work I'd rather spend my time on which pays better. But I want to do it as professionally as possible. So today I'm delivering the work which we've agreed on so far. My plan is to send it with the final invoice and a note saying that I'm booked up, so am giving her all the information she needs to take it forward herself or hand it on to someone else. But what's the best way to word it that makes it clear that this is 'good-bye' but which doesn't leave an unprofessional impression? She is a close contact of other clients of mine whom I like and respect. Help?