I guess it would depend on whether this is your business or a favor. Also, does she have a lot of $$? and, whose idea was it? I would certainly have her buy the fabric and supplies. I would never charge my MIL unless I was doing it professionally and they were a real big deal, like drapes, in which case I would help her shop for them, rather than make them :) I would say, happy birthday or mother's day or something. Charging family is such a touchy thing, isn't it?