I don't see any outstanding flaws with the grammar. So I would say it is correctly written.
Answer:
D. Many a happy hour she had spent planning for something nice for him.
Explanation:
From the given excerpt, the loving and caring nature of Della has been evoked. She is continuously thinking and saving money so as to gift her husband the golden chain. Her love for him can not be measured by the amount of money she is intending to save. It is the feeling hidden behind her sacrifice that counts. She has been saving for months so as to make him happy on the Christmas day. All her activities and actions are inclined towards saving and planning for the gift. This reveals her true feelings for her husband.
My best choice for this would be A.
