Is a daughter considered sinful for not sitting and talking with her father—whom she cares for after her mother's death—due to his harmful actions toward her and her children, which make serving him difficult for her, despite her fulfilling all her duties of care and service?

Caring for and serving one's father when he is in need is a required act of piety and among his rights. One must be patient with one's father and his misbehaviors, especially in old age and illness, for Allah Almighty says: "And your Lord has decreed that you worship none but Him. And to parents, do good. If one of them 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 nurtured me when I was small.'" There is no blame in not sitting with one's father and refraining from speaking to him if his harm is feared.