Am I sinful because of my arguments with my deceased mother, and what is the expiation for that, knowing that her death occurred as she had prayed that I would not be present for it?

Filial piety is among the most emphasized duties, especially in old age. It is not permissible to scold one's parents or to quarrel with them. What you did towards your mother is unacceptable and contradicts Islamic law. You must promptly repent, show remorse, seek forgiveness, increase your acts of obedience and supererogatory worship, and pray for your mother's mercy and forgiveness.