Is feeling inner distress and sorrow considered a sin when a father favors one of his daughters in treatment and giving, while maintaining affection and kinship ties?

We have previously clarified the ruling on parents favoring some of their children. You must continue to honor your father and maintain ties with him. His favoritism towards your sister does not justify treating him differently. There is no sin upon you for the sadness in your heart resulting from his treatment, because the actions of the heart are beyond one's will, and "Allah does not burden a soul beyond its scope."