Morally she shares some responsibility, after acknowledging that her son was a mental case and knowing full well of his temperament and ownership of more that a dozen firearms, she should have tried to get help. But there is no crime on her part.
I don’t know if Mom tried to get him help or not, but I can tell you that it isn’t easy. Law enforcement doesn’t intervene until a crime is committed. Our mental health system is a joke. Unless the patient agrees to treatment, there is little a family can do.
She could, however, have made sure he didn’t have access to firearms.
I speak from years of experience. Our family’s situation is now solved by incapacitation unrelated to mental issues, but there have been many times in recent years that I’ve said, “There but for the grace of God go I.”