welcome to health care magic
I can easily understand your situation and i appreciate your effort to seek online help. Schizophrenia
is a chronic condition characterised by delusions, hallucination and other psychotic symptoms. Hearing voices are auditory hallucinations
which are characteristic of schizophrenia. For this various drugs like antipsychotics are available which are quite effective. Before labelling as "drug resistant schizophrenia" and thinking of other options like ECT, one must give a trial of clozapine
which is gold standard in drug resistant cases. I don't know whether your mother has been put on clozapine. But this is must. Discuss all this with your doctor. ECT is the last option considered.
Hope it helps
Dr. Gourav Monga