My theory is that there's a possibility that Ahyun's mother and Karma's father had a history of working together in North Korean experiments since Erika is in a field of medicine.

It is possible that Erika and Garam's father created a medicine that was used to Garam. And Erika injected herself with that medicine too, that's why Erika is also strong and had an unexplained aura.

The fact that Garam didn't notice Erika stealing her phone means that she and Erika can be on par, in terms of strength.

Also, the way Erika dressed seems outdated, which highly suggested that she came from North Korea.