My sister is being tormented from within. Somedays I believe this reality is a game or a play. I don't believe it. It's just useful. So maybe externalizing the voices might be helpful for her.
I wish I knew the natural variance of outcomes. Suicide is a real risk. She has told me so. Read the research. Being a psychiatrist is a dangerous job, especially within a prison or mental health facility. So schizophrenics can be dangerous. She needs help. There is no help. No cause, no answers.
R D Laing who wrote The Divided Self said that the most sane people were those who couldn't or wouldn't go along with this insane world. I'm not qualified and don't know how it is for your sister, but I'm also not convinced that psychiatrists have the answer, they seem stuck in their own professional concepts, too conventional and trying to 'normalise' everyone. I think we must stop trying to fit into narrow, fictional 'ideals'. If there is emotion, anger or tears, there is a need not being met, the frustration of that must drive people to react, and if that's dangerous for a psychiatrist it makes me think they've missed something, such as treating people with honesty and true respect.
When I 'heard' things in my head it was usually some critical, self-abusive comment but I eventually practiced recognising it, detaching and evaluating if it was a fair comment I agreed with and needed to work on or was unreasonable and nonsense. Some days I just say "nope, not listening to that". It is hard and very scary trying to make sense of your mind, with your mind, and takes time. Now I have few only very trusted friends, can't take dishonesty or any sense of an alternative agenda with people, and took a vow to love respect and trust my Self. I actually enjoy being with my self and we often have a laugh! Recovering self-worth in your own eyes is a first and vital step.
The times I didn't want to go on, I always had someone who would be devastated (currently it is my daughter) which always stops me contemplating that 'option'. You sound like a lovely brother, I'm sure it is you she'd stay alive for, don't be afraid to let her know that, it's just not an option, she has a responsibility to you and your happiness, as well as to her Self, I'm sure she knows this. As we get older, we get better even at this game called life. We learn ways to get through. I dance or consult my I Ching which makes me have to meditate. It is my intuition that has the answers.
This must all sound very lightweight in the face of powerful trauma that has led to your sister's torment, but remember all things pass, even emotional states only last 90 seconds if we sit and make friends with their innate wisdom. Deep down we know ourselves better than anyone else does and know best how to love who we are.