It seems that the production of anything to do with beauty, whether it be art, dance or home decor is dismissed as frivolous and the person doing it is less intelligent.
It takes a brain to be creative and to visualize a design that works. Not everyone can accomplish this.
I liked how Sally's reading interests was pointed out that it took some intelligence to comprehend.
It seems no matter what Sally accomplishes, though, she is stuck competing with her sister. It also seems her sister is jealous of her. Why else would the sister be so disparaging?