I think there are some quilts out there that should not be used. By that I mean they have either sentimental value (made by or for a loved one who has since passed away) or are old and/or valuable. Those I think can be displayed but a quilt that was made in the 1800s would not be a quilt I would recommend for use on a children's bed or for a picnic blanket. I think most quilts are made to be used and loved until they are well worn out but there are exceptions and I think such quilts should be recognized as being precious enough to not use until worn into pieces. Just my opinion.
crafty: If your MIL is afraid to use it, suggest she buy a clear plastic table cloth to go over it. I have a beautiful lace tablecloth (now packed in a box somewhere from the last move) that I do this with. I would not be happy if it got stained but I still want to use it so I compromise and put a lightweight plastic tablecloth over it. This way I can still display it and others can enjoy it but I don't have to worry about it getting soiled or worse, snagged and ruined.