Irene Tung and Steve Lee, from UCLA psychology, conducted a research review concluding that girls with ADHD are more likely to have issues with defiance and acting out than problems with depression or anxiety. Girls with ADHD are more than 5 times as likely to have oppositional defiant disorder and more than 9 times as likely have conduct disorder. Across the general population, depression and anxiety are more common among girls, which creates the assumption that girls with ADHD would be more likely to exhibit depression and anxiety. This assumption stems from the fact that the majority of ADHD research focuses on males. By having more awareness of this co-morbidity specific to females, we can more effectively diagnose and treat ADHD.
Source: Girls with ADHD often struggle with defiance, conduct issues Reuters, 21 Sep 2016
Additional coverage on this research:
An ADHD diagnosis puts girls at much higher risk for other mental health problems UCLA Newsroom, 04 Oct 2016