Hello,
Hearing of voices which arte not there are due to auditory hallucinations.They are typically found in dissociative identity disorder(or multiple personality disorder) and schizophrenia.
Cymbalta which is an antidepressant when used for a long time or on overdose can cause worsening of depression and causing of other psychiatric comditions like suicidal thoughts and anxiety.
I feel that a consultation of a psychiatrist will be the best.
Hope it helps.Take care and pls do keep me posted on how your grandmother is doing.