You don't know to what degree she is mentally ill. My mother is schizophrenic effecitve as well and she does terrible things all of the time because she hears voices all of the time. She does not know what is real or what not. When she believes someone is trying to hurt her or do something or anything that her voices tell her that is her reality. If she hears a voice tell ehr a conspiracy that is real as day. If it is someones fault based on face that is equally real. You can not convince her otherwise. My mother is in no way functional nor can she in any way be a valid member of society even on her best day.

You are taking one example one causation and assuming that is the answer to every single person in the same scenario and that is terrible logic. That is the same as saying all dogs have tails so if it has a tail it is a dog.

All mentally ill people are functional to different levels. So likewise you do a diservice in assuming they all can be accountable. This appears to be the age when mental illness first sets in. You do not know what she has and to what severity. It might just be setting in now as well. Which means it is getting progressively worse.