If you are going to do a quilt on commission, then it's a job. And like any job,you need a contract that both you and the other party sign. Do research, give her an estimate of costs of materials and then give her an estimate on how much you charge for labor. Do NOT skimp on the labor costs. This is a job and you need to be compensated for your time and expertise. If you go into this job with the idea that you are not good enough, then you will not be compensated fairly for your labor. I think sometimes we think that because we can go and make a beautiful handcrafted when ever we want to, sometimes we think that it's not really that important. First of all, not everyone can take some fabric, thread,batting and binding and turn it into something not only beautiful, but useful as well. When my Dad was alive, he did all the repair work on all our vehicles. Our vehicles never saw the inside of a mechanics shop until he had a stroke and could no longer do the work. Well, I found out real fast how much the work that my Dad did on all the family's vehicles truly cost in the real world. The same is true of your ability to make quilts. Do not undersell yourself or your ability.