I would wait before even thinking of making a memory quilt. The SIL needs time for grief and that may take a year or couple years. Don't rush in as this M quilt could open some buried memories of the SIL. A comfort quilt would be the best at this point. Later, talk with your brother, don't forget he also is experiencing his wife's sadness. I'll pray for SIL's healing and her sadness. For now, just be there for her.