99% of the time people do not intentionally not pay. In this case you are even aware of the circumstances. My philosophy is, and always has been do not clean windows for free, ever, for any reason, but in this case that's not what you would be doing, you'd be granting a loyal customer leeway on a debt that she has found herself unable to pay.
Obviously I don't know the intricacies of your relationship with this customer but on the face of it I'd be inclined to let the debt slide, for a wee while at least.