The heroine, Sybylla Melvyn, is an imaginative, headstrong girl growing up in rural Australia in the 1890s. Drought and a series of poor business decisions reduce her family to subsistence level, her father begins to drink excessively, and Sybylla struggles to deal with the monotony of her life. To her relief, she is sent to live on her grandmother's property, where life is more comfortable. There she meets wealthy young Harold Beecham, who loves her and proposes marriage; convinced of her ugliness and aware of her tomboyish ways, Sybylla is unable to believe that he could really love her. By this time, her father's drinking has gotten the family into debt, and she is sent to work as governess/housekeeper for the family of an almost illiterate neighbour to whom her father owes money. She finds life there unbearable and eventually suffers a physical breakdown which leads to her return to the family home. When Harold Beecham returns to ask Sybylla to marry him, she concludes that she would only make him unhappy and sends him away, determined never to marry. The novel ends with no suggestion that she will ever have the "brilliant career" as a writer that she desires.

Question: Harold Beech asks Sybylla to marry but why does she refuse?
Answer: Unable to make him happiness. 
Alternative answer: she doesnt believe him