I am sorry to be a meanie ... But the next ime you have to go shopping at a local quilt store, take her along to see what a quilt costs to make these days. That should raise her eyebrows a little.
There are many people who just don't understand about quilts. Probably because they were out of fashion for a while and the process was not seen day in and day out on a quilt frame with a dear lady blistering her fingers to finish a hand made, hand quilted coverlet.
Have them watch the antique road show. These old beauties go for a hefty sum! Thousands. Some of the new ones go for that amount too, I might add. Just visit a shop that sells them. It is jaw dropping at a checkout stand of a quilt shop.
Ranting aside ... You are a sweet mother in law to forgive her so quilckly. God willing we were all so nice.