Bullying among girls is often subtle and relational, which can go unnoticed by parents, teachers and healthcare professionals. This article explores how covert aggression – such as social exclusion, gossip and emotional manipulation – can cause profound psychological harm to targeted girls, many of whom may not even realise they are being bullied. Through an analysis of defining attributes of girl-to-girl bullying and general implications for mental health, this article aims to highlight the importance of early identification and treatment. The article also points out how social patterns of bullying found predominantly in girls’ social circles carry over well into adulthood, emerging in the work environment, social circles and cyberspace. Focused on practical application, this educational paper aims to enhance clinicians’, caregivers’ and teachers’ recognition of relational aggression, develop collaborative approaches to prevention and facilitate useful interventions for those affected. Ultimately, increased sensitivity to subtle bullying has the power to reduce subsequent harm and result in healthier social contexts.