Let me ask something, if you were a dentist and knew your Mother in Law needed a bridge, you gave her the gift of prep, etc. of a bridge for a gift. That would be a valuable gift wouldn't it?
That is something everyone can relate to value. Quilts, and sewing are often thought of as someting inexpensive-that we just whipped up! Unless the reciever understands the value of a handmade gift, they won't truly appreciate it. If your SIL is like your MIL you may want to re-think your gift. If you think you may get the same kind of reception from your MIL, you may want to wait, until she has a clue! Take them to a quilt festival, or a quilt museum.