My wife works and has an independent income. Her father is elderly and financially incapable of making hajj and 'umrah and his male children are unable to help him in this respect. My wife (and I agree with her) wants to give her father a sum from her own money that suffices for the expenses of hajj and 'umrah. Both my wife and I have performed our obligatory hajj. Is it legally permissible for my wife's father to perform hajj or 'umrah from his daughter's money?

There is no legal impediment if your wife pays for her father's hajj or 'umrah from her own money. This is out of dutifulness, benevolence, and maintaining ties of kinship. By giving money to the donee—no matter who he is—the money is transferred into his ownership and this fulfills the condition of capability that is necessary for hajj. God the Almighty says,

Pilgrimage thereto is a duty men owe to God,—those who can afford the journey. [Al-'Imran, 97]