Will Allah hold me accountable for my shortcomings in teaching my mother about her religion, knowing that she is Muslim by name only and does not fulfill all the obligations such as prayer and hijab?

As long as the mother has pronounced the two Shahadas and observes fasting, the original presumption is that her Islam is sincere. It is obligatory upon anyone who knows her situation to strive to teach her the matters of her religion, especially prayer, and to explain its significance. This education is considered Fard Kifaya (a collective obligation), and if there is no one else, then it is obligatory upon you to undertake it. Teaching the mother and guiding her to the straight path is among the greatest acts of righteousness towards her. Wisdom and gentleness should be exercised in teaching her, and assistance can be sought from scholars.