Final answer:
Louisa's error is her failure to communicate her true feelings and desires to Joe.
Step-by-step explanation:
Louisa's error can be described as her failure to communicate her true feelings and desires to Joe. Instead of expressing her own inclinations, she resorts to diplomacy and attempts to sound him out without revealing her own thoughts. This creates a difficult situation as both Louisa and Joe are afraid of betraying themselves. She never mentions Lily Dyer and simply states that she has no cause of complaint against Joe but shrinks from making a change in her long-standing way of life.