Is the father obligated to provide for his daughter, who is 18 years old and has left him, abandoned her religious duties, and gone to live with her apostate mother, knowing that American law lifts the obligation of financial support upon reaching this age?

A financially capable father must provide for his needy daughter until she marries. The fact that the daughter is not religiously upright does not negate the obligation of financial support, as it falls under the category of maintaining kinship ties, which is commanded by Islamic law. This does not entail befriending those who oppose Allah and His Messenger. Allah has commanded maintaining kinship ties generally and condemned those who sever them. Providing for a needy relative is one of the greatest forms of maintaining kinship. Analogizing financial support to inheritance is a flawed analogy, as disbelief does not nullify kinship rights in this world, including financial support when needed. It is advisable to intend this expenditure as a means of softening the daughter's heart towards righteousness, seeking reward from Allah.