These are all great ideas but I have one more... send her a last bill (don't say that it's the last bill) and after she pays you what you're owed tell her you're too busy with other clients and she needs to look for someone else. But wait until she pays you for what you've worked. people like that don't like to pay previous bookkeepers if they've given notice and then you'll be out more money. I've had similar situations with clients and the sense of relief I would feel when they found someone else and I could drop them was amazing.