Faith is established to be a practicing Wiccan, and texts to Sara shows that she truly believes that she is one. Other texts also imply that she has attempted to trick Sara into coven initiation in the past, something the latter clearly doesn't like. While Faith's attempts at pressuring Sara into her witch activities are certainly overbearing, she was likely only trying to include her friend in her beliefs, not meaning her any harm until.......
When Faith shows up at the jungle that fateful night for the Walpurgisnacht, she runs into Irizu's cult (instead of the frat boys she expected to find). Faith believes she's finally encountered real witches, and tells Irizu that she wishes to join. Like with our player character, he tells her that she must be initiated by offering a human sacrifice. Faith, all too eager to be recognized as a "real" Wiccan, betrays Sara revealing to the cult that she had invited her to the party. After Irizu and the cult capture Sara, they turn on Faith, rubbing it in that they saw her as nothing more than a joke, and found her more useful as a Human Sacrifice.
Before Sara's capture, she was already in the jungle when she opened that James had sent hernote . Assuming that Irizu was already controlling Sara's phone through IRIS, it's likely that the video she dismissed as corny was actually a supernatural GPS that allowed Irizu to pinpoint Sara's exact location. The real-life Malaysian jungle where Sara went missing is huge, so trying to find a human in there without assistance would be like finding a needle in a haystack. This, coupled with Sara's paralyzing fear that slowed down her pace, made it easy for the cult to track her down and capture her.
If (sorry, when) you reach the cult's location via the sent coordinates, you will find Sara still there, beaten and traunatized. Assuming Irizu keeps his promise of welcoming you into the cult, you use your newfound position to dismiss Sara (during which you give her back her phone, and break to her the awful news about James). You will also have to help dispose of Faith and James' bodies.
- You're assuming the good ending is the canon one. Or that they'd let Sara go. Remember, anyone who finds out about the cult either is killed or joins them.
