Well, you have already set yourself up as very very inexpensive. I know you want to be fair to her. Does she also want to be fair to you? If so,then she should pay a fair price.
You could google "upstate NY" and "longarm quilting" and see what quilters in your region are charging. Some longarmers have a calculator on their website so you could just type in the width and length of the quilt and see what their charge would be. Then you need to decide how much you would be willing to charge for your time and talent to do the same stitching.