Mayberry is a staunch advocate for gun control in the United States. Following the Sutherland Springs church shooting, Mayberry released a video on her Twitter account criticising President Trump's response, arguing that "it’s somewhere on the scale from ironic to disgustingly hypocritical that Donald Trump is talking about mental health with regards to this attack when his administration has done nothing but try to restrict access to help get care for people who need it the most". She further recounted her memory of the Dunblane massacre in which 16 children and one teacher were murdered with handguns, resulting in sweeping gun control legislation in the UK. Mayberry credits these efforts with substantially decreasing the number of mass shootings in the UK.