Is the mother justified in feeling guilty for her shortcomings in raising her children who have abandoned prayer and mistreat her, and will she be held accountable for shunning them despite her efforts to teach them matters of their religion?

If you have fulfilled your duty in raising your children, then there is no sin upon you for their disobedience, because guidance is in the hands of Allah, and no soul shall bear the burden of another. It is permissible for you to shun them for disciplinary purposes and to deter them from abandoning prayer and from misbehavior. The sin of shunning a Muslim for more than three days does not apply to you. Usually, it is better to maintain ties and show kindness, while persistently enjoining good and striving to reform them, rather than shunning them. Strive to reform them, do not despair, seek help from righteous people, and supplicate frequently for their guidance, for a parent's supplication for their child is answered.