Maybe I am too laid back, but I would (and do) just walk away.
The windows won't stay clean for ever, and when she begins to see the dirt accumulating on the windows, it will be a constant reminder to her of what she did to you. I would tell other w/c's too.
There are enough good customers who will value your service to allow you to waste time chasing after one wrong'un. You will end up spending more money chasing, than what the job was supposed to pay in the first place.
John.