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She should consult a psychiatrist. The symptoms like possessiveness, ideas, or even delusional beliefs about the fidelity of husband, blaming husband, etc. cannot be ignored. She might be suffering from some mood disorder most likely depression with psychotic symptoms. This could be some psychosis too. Individuals with psychosis show paranoid delusions, delusional beliefs, and become suspicious. Considering her age and late onset, the chances of depression with psychosis are more.
She might refuse to visit a psychiatrist and will try to evade the visit. Drugs like Olanzapine or Quetiapine can be used to reduce her psychotic symptoms, and she will come out of depression.