How can I teach my illiterate mother the basics of her religion, such as creed, given her difficulty in memorizing classical Arabic terms, and my lack of knowledge in the jurisprudence of teaching and enjoining good?

The religion of Allah is easy and aligns with human nature. An unlettered person can learn through instruction and listening, as happened with the Arabs during the time of the Prophet, peace and blessings be upon him. It is not obligatory for a Muslim to memorize the eloquent words of scholars. Rather, what is obligatory is to believe in the truth and act upon it. For memorization, it suffices him to know Al-Fatiha and what is necessary for his prayer to be valid. The questioner can convey what he knows to his mother in the language she understands. If he lacks any obligatory knowledge, he must learn it first and then teach it to her.