McCartney pleaded guilty to a litany of child sex offences and the manslaughter of 12-year-old Cimarron Thomas, who took her own life minutes after an online chat with him in 2018.
More than 3,500 victims were identified in Belgium, Canada, Croatia, Colombia, Denmark, Germany, Italy, Latvia, Lithuania, Mexico, the Netherlands, Norway, New Zealand, Poland, Slovakia, Spain, Sweden and the US as well as the UK.
McCartney, who is from Northern Ireland, posed as a teenage girl called Chloe to trick Emily and others into sending photographs.
He would then use a pre-typed message to reveal himself as an online predator.
“My heart dropped out of my chest,” said Emily.
“And I just felt my whole world collapsing around me. It was very scary.”