she meets a man named Hae-Joo Im, who it is revealed was behind her friend, and then her.
What does this mean behind her friend, and then her?
We need more context. It is not clear from the excerpt you provided. We look further
[...] Hae-Joo Im, who it is revealed was behind her friend, and then her, being exposed to something more than their day-to-day existence.
In this instance
Behind can also mean responsible for or causing
So Im was responsible for exposing to the clones to experiences other than their daily Papa Song jobs. In particular, it is implied that Im is responsible for the clones finding the cellphone and using it to watch the fragment of the film "The Ordeal of Timothy Cavendish".