I think you are right and it is real young ladies that show affected indifference in Ch. 5. I must say how dishonest of them. Not all is lost however. I think Catherine can be said to patronize another heroine in her defense of Udolpho unlike the usual heroine. Catherine also differs from novel heroines as her feelings about novels are far from disgust:

Yes, novels; for I will not adopt that ungenerous and impolitic custom so common with novel–writers, of degrading by their contemptuous censure the very performances, to the number of which they are themselves adding — joining with their greatest enemies in bestowing the harshest epithets on such works, and scarcely ever permitting them to be read by their own heroine, who, if she accidentally take up a novel, is sure to turn over its insipid pages with disgust. Alas! If the heroine of one novel be not patronized by the heroine of another, from whom can she expect protection and regard? (Ch. 5)