Is it obligatory to be dutiful to a Christian woman who adopted and raised me when I was young, knowing that I am from a Muslim family and have embraced Islam, while she has remained steadfast in her religion, and she is now elderly?

It is permissible, according to Islamic law, to be righteous and kind to a non-Muslim woman, as long as she is not hostile towards Muslims. This is based on the Almighty's saying: "Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly." (Quran 60:8) Al-Bukhari cited this verse under the chapter "Giving Gifts to Polytheists" and mentioned the hadith of Asma bint Abi Bakr concerning her maintaining ties with her polytheist mother. And among the greatest acts of kindness towards her is inviting her to Islam, as the Prophet, peace and blessings be upon him, said: "For Allah to guide a single man through you is better for you than red camels."