Even with schizophrenia the voices do hear in your head. I actually hear voices outside and inside my head. I guess it's a matter of what medication works. She's probably thinking if a certain medication worked on your mother than possibly it can work for you... or maybe these voices will die down with anti-psychotics because some may be caused by psychosis. I'm not familiar with how they treat DD and I'm not a professional. It's possible to have both.