When teaching a new nursing aide (nurse) in the nursing home setting, most often they get it (the finer points of helping the patients). Some take awhile and few have to be re-educated.
Take this sil to a quality quilt shop and have a list of things she needs to buy for an imaginary quilt. Have her write down the prices of each item. Already have price of labor figured in and let her do the math. If she does not get it, she never will.