CIs does not cause Schizophrenia. Your friend may have developed Schizophrenia on her own without CIs - there may be a different cause but the timing just happened to happen AFTER the CI surgery which may have made her think that the CI surgery caused the Schizophrenia.
Some people with Schizophrenia or other mental illnesses do not like to share with others the fact that they have a mental illness because they feel VERY embarrassed and there is a HUGE stigma linked to mental illnesses. A lot of non-mentally ill people look at mentally ill people as if they have leprosy and either are afraid of them or think they are strange or whatever. But they are not strange (they may act strange when off meds, but on the proper meds they can function pretty well). They would appreciate some support and open mindedness and understanding and some patience. Once you get to know them, they can turn out to be pretty cool and interesting people, and they often have a deeper understanding of things because they understand what it is like to have a mental illness. The only times they may become too strange or scary is most likely due to not being med-compliant or not on the proper meds (not one medication will work for ALL Schizophrenics - each person's brain is DIFFERENT and responds DIFFERENTLY to the same medication). Once the right medication combo/cocktail has been found, usually there is a big success in gaining back function of life and activities and stuff and they can live pretty much normally as long as they take their medication religiously. Mentally ill people who are off meds and those who are on meds, the differences are like night and day, trust me. I know a couple of people with Schizophrenia and I have seen a huge difference in them once they have been on the proper meds for a long period of time (it can take a while for the medications to have full effect - it cannot just happen overnight). Mental illness is no one's fault - it is because there is a problem with the chemicals in a Schizophrenic or other mentally ill person's brain. There is a huge stigma because people see someone acting very bizarrely off of meds and end up painting the entire mentally ill population with a very broad brush just because of that. That's not fair to do that.
I have a very dear friend who has both bipolar and Schizophrenia...but she has been off of her meds so she has been behaving very bizarrely lately, to the point of scaring other people and doing very inappropriate things. Someone is taking care of her (as in making sure she has a home and food) but no one is doing the right things to make sure she gets the proper care she needs. She's been in and out of the hospital. I am extremely concerned about her but unfortunately I am 6 states away so unfortunately I can't really do anything about it. She's someone I grew up with ever since I was 4 years old, so she is a very dear friend, and it makes me VERY sad to hear that she is NOT doing well. I cried when I got this news about her from another friend. Fortunately I might have a way to help her, I have an idea, but I have to discuss this with my other friend first.
Anyway, it is NOT possible for CIs to cause Schizophrenia. That's a fact.