Clara Amedroz is the only surviving child of the elderly squire of Belton Castle in Somersetshire. At twenty-five, she is old for an unmarried woman. Her father's income and savings have been dissipated to pay for the extravagances of her brother, who subsequently committed suicide. Since her father has no living sons, his estate, which is entailed, will pass upon his death to a distant cousin, Will Belton.
Despite her poor prospects, she has two eligible suitors. Within four days of making her acquaintance, Will Belton proposes marriage to her. Belton is warm-hearted, kind, and generous, and these qualities make a strong impression on Clara. However, she believes herself in love with Captain Frederic Aylmer, although he has given no clear signs of feeling that way toward her. Aylmer is impeccable in his manners, smooth, urbane, well-read, and a member of Parliament; compared to him, Belton is awkward and unpolished.
Clara rejects Belton's offer, urging him to regard her as a sister. Not long thereafter, Aylmer proposes to her, and she eagerly accepts. However, her happiness is short-lived. Her new fiancĂŠ proves shallow and cold, more concerned with his own comfort than with her happiness. Moreover, he expects her to subject herself to his domineering mother.
Mr. Amedroz dies; and although Belton offers to allow Clara to remain at Belton Castle, she goes to live with the Aylmer family in Yorkshire. Lady Aylmer, who wants her son to marry money or a title, exerts herself to make Clara miserable there; and Captain Aylmer offers no support to his betrothed.
For Clara, the final straw comes when Lady Aylmer demands that she sever her ties with a friend. Mrs. Askerton, Lady Aylmer has learned, left an abusive drunken husband in India and lived with Colonel Askerton for several years before the death of her husband freed her to marry him. Clara is duly appalled by her friend's past immorality, but cannot bring herself to cast off someone who has come to depend on her friendship. Pressed relentlessly on the subject by Lady Aylmer, she declares an end to her engagement and returns to Somersetshire, where she accepts the hospitality of the Askertons.
Will Belton has never ceased to show his love for Clara, and she realises that he is worthy of her love. However, she believes that it would be wrong to transfer her affection from one man to another. Only after Mrs. Askerton and Will's sister Mary Belton persuade her that it would be unjust to withhold her affection from Will can she bring herself to put aside her scruples and accept him. Marital bliss ensues.

Question: Why does the estate pass Clara and instead go to Will Belton?
Answer: Because her father has no more sons, and it cannot go to a daughter. 
Alternative answer: She is a woman.