Ok, this is why we have PL insurance.. (and I hope everyone else here has it too...)
My broker says to sit and wait and see if she instructs a solicitor in this regards, and to admit nothing, which I'm not.
If she tries to sue, my insurance will cover the costs if she is successfull or not.
I have cleaned thousands upon thousands of windows for hundreds of people! Why this and why now?!!!
Glad to be insured, I can tell you.
I'm locking this now as I don't want anything else said on the matter, but thanks for the feedback/ideas Gold and others.