Is it permissible for a father to favor his son over his daughter, who works with him and excels in her life, despite the psychological impact this has on her, and is she allowed to discuss this matter with him?

The father should fear Allah and be just among his children, because injustice causes hatred and disobedience (to parents). This is why the Prophet, peace and blessings be upon him, said: "Fear Allah and be just among your children." However, injustice does not justify disobedience to parents. Therefore, you should be patient and dutiful to your father, and try to guide him gently and kindly towards justice, or through those whom he trusts, and avoid arguing with him.