If people don't know what goes into a quilt, or, if they assume that a quilter (or other kind of crafter) is just sitting around waiting to be asked to make the thing they make, I guess we can't really fault a person for asking if we will make them one. From our informed perspective, it seems like a nervy thing to do, but from the perspective of not knowing anything about it, it's not so bad. But that makes it our responsibility to say no (if we don't want to do it), and to educate the person asking, about the time and money that goes into a quilt. I wonder what SIL would have thought/said if you'd responded, 'It would take 6 weeks of my leisure time and $200 worth of fabric to make you a quilt.' Perhaps she would wonder why you would want to spend that kind of time and money on someone who isn't part of your life.