What is the ruling regarding a girl who is unable to express feelings of love for her father, and feels repulsed by his unwise actions and his talk about marital relations which offends her modesty? Is it sufficient for her to buy him gifts to fulfill her duty of righteousness towards him?

The hatred you feel in your heart for some of your father's actions does not justify ill-treatment. Rather, you must be dutiful and kind to both parents, for Allah Almighty says: ﴿And your Lord has decreed that you shall not worship except Him, and to parents, good treatment. Whether one or both of them reach old age [while] with you, say not to them [uff] and do not repel them but speak to them a noble word. And lower to them the wing of humility out of mercy and say, "My Lord, have mercy upon them as they brought me up [when I was] small."﴾ [Al-Isra: 23-24]. The actions you dislike may be natural, especially since a man still has his desires even if he grows old. Your inability to express your feelings and staying away from him exacerbates the problem; your closeness to him and your kindness towards him give you an opportunity to guide his wrongful behaviors. Gifts are not enough, for the psychological and emotional needs of an elderly person are more important than material things. The father should be brought out of the emptiness of retirement by occupying him with social activities, companionship, or a small project. This will improve his psychological state and eliminate problems. Be kind to him, and you will find goodness in this world and the hereafter, for the father is the middle gate of Paradise.