Why is Nancy concerned about her father?

Nancy was concerned about her father because he seemed to be in a perpetual bad mood. During her conversation with Susan on the phone, Nancy mentioned that her father did not seem like his regular self. She complained that he always seemed to be in a bad temper whenever she was around. Nancy was becoming concerned because her father's strange, emotional behavior had been going on for three weeks.
Nancy confided in Susan that her father was greatly displeased with her decision to continue seeing Bobby, her boyfriend. Part of Mr. Clutter's concern lay in the fact that Bobby's family was Roman Catholic, while the Clutters were strict Methodists. Although Nancy loved her father, her relationship with Bobby was driving a wedge between her and her father. 
For her part, Susan advised Nancy to reason with her father. However, Nancy did not think it would do any good to further discuss her feelings with her father. Whenever she had tried to enter into a rational discussion with her father, it had always ended poorly.
Nancy complained that her father was often unyielding and unreasonable about Bobby. Nancy was concerned about her father because his bad temper appeared to show no signs of abating; she was worried that her father's anger would negatively affect their relationship.