Is she supplying the back, batt and thread or are you just doing the top? If she wants you to do the whole quilt then you will need to charge something for the things you will have to buy. I would look at the box of fabric before agreeing to it for payment. If it is a large box with lots of large Quilter's quality pieces of fabric, it may be adequate if your stash is low. If your stash has more fabric than you can possibly use in this lifetime, then work out payment plan instead.