That's an individual experience, not scientific proof. An experience limited to school kids of a certain age and location who share their problems with your wife.
No. She cited what was taught during her studies (she got her license 3 years ago, so the studies have all been within the last 10 years). According to what she was taught, Most mental illnesses correlate positively with lower IQ (apart from neurodevelopmental disorders, which this study measured, and bipolar disease).