Marina hacks the technology of the people she wants to mess with and eventually kill.
Marina makes it impossible for any of the people involved to delete their Facebook profile or posts she makes.
Marina was able to get the video footage from the elevator and footage from the hospital.
Marina was able to enroll into the university with a fake name.
When Marina became Laura's friend on Facebook, she was basically able to see Laura's whole life and see where she was. When it was Laura's birthday and Marina wasn't invited but she knew what restaurant to go to because of the post Laura's other friends had made and had tagged Laura in.
Facebook's tagging system made it possible for Marina to tag all of Laura's friends when she uploaded each video on Laura' s account.
On one of Marina's posts she tagged a website, from there Kobe was able to discover how Marina was accessing people's social media accounts and computers (by virtually haunting them) and ultimately a way to stop her.
When one of Laura's friends became Marina's friend on Facebook, they knew they were going to die.
Laura and her friend find an old school picture of Marina and from there are able to find the school. Laura goes and talks to the headmaster and discovers Marina's real name. With the full name, Laura's boyfriend is able to find her medical records to discover Marina's and her mother's medical information from an accident. Laura then looks up the incident and are able to find where Marina and her family used to live.