Hi honey, so sorry to hear you've had such a rotten experience. (If you had pressed harder, she may well have complained you did some damage(!) ) Take pride in the fact you stuck to your guns while still taking her wishes into account - that's being professional!!!
My first thought, also, was that this woman was trying to get out of paying. Ah well. It's not a good way for her to live, and will not be doing her any favours, however it must seem(!)
One thing that works for me is the old, write a furious letter you don't send, trick. Just get it all down on paper. Apparantly, through some psychic 'link' we all have, the message gets across!
All the best xx