As an insurance adjuster, I guess I have a different perspective on this one. If you are installing shingles "knowing" that they are not going to seal for some time, then, you're sticking your neck out.
Think of it this way, if you go to court over this and you acknowledge that you are aware the shingles installed may not seal because of the time of the year,then, you will lose every day of the week.
Any decent attorney would make you look either incompetent or greedy at the expense of the "poor" homeowner. As an insurance adjuster, if that homeowner filed a claim for her wind damage, we certainly would pursue subrogation against you.
I would suggest the following. Contact the customer and apologize. I'd throw out the option of getting a local independent engineer to look at her roof to ensure that it is structually sound or offer to seal er shingles with mastic. Either way, it may cost a couple hundred bucks, but, it may save you a lot of aggravation down the road.