Concepts like this can certainly be due to mania or psychosis, so maybe read about bipolar disorder a bit. Good stuff here on the site. Generally, if she is psychotic or even more so manic, trying to "reason" with her will likely go nowhere unless she gets treatment. One of the problems in mania is that the part of the brain that controls certainty is basically on fire. No words will convince otherwise, take it from an expert. Best of luck.