Yes, it could have been the cult coming after her and yes they might have forced or coerced her to return or killed them all but it could also have been no more than some stranger that they almost hit and the rest could be Martha's intensifying paranoia constructing what we were seeing.
The goal though was to get the audience to ask these questions but I think Durkin failed in defining the intent of posing this question which was to illustrate Martha's own confusion and uncertainty about her paranoia, not the audience's confusion about what happened. I could possibly suggest that he use a tighter close up on Olsen to capture the nuances of her expressions showing her fear and uncertainty but I think he tried to use a different tactic...
Note that at times of her most paranoid, she is visually alone in the scenes. In the back of the car we don't see Ted and Lucy in the front seat. At the dinner party she is alone with the bartender despite the fact that there were dozens of people nearby. During her final swim she is alone when she sees the man sitting across the lake watching her. Even when she awakes in a panic and pushes Ted down the stairs we don't see his face or Lucy until after the fact. When she breaks the window on the black SUV, when she hears the pine cones hitting her window at night... she is alone.
I think we as an audience just weren't offered a way to tie our own questions with Martha's state of mind. Maybe if there was a scene in which Martha asks these same questions to Lucy. Maybe if they shot from a first-person perspective. I don't know but it just didn't quite work for me.
The goal though was to get the audience to ask these questions but I think Durkin failed in defining the intent of posing this question which was to illustrate Martha's own confusion and uncertainty about her paranoia, not the audience's confusion about what happened. I could possibly suggest that he use a tighter close up on Olsen to capture the nuances of her expressions showing her fear and uncertainty but I think he tried to use a different tactic...
Note that at times of her most paranoid, she is visually alone in the scenes. In the back of the car we don't see Ted and Lucy in the front seat. At the dinner party she is alone with the bartender despite the fact that there were dozens of people nearby. During her final swim she is alone when she sees the man sitting across the lake watching her. Even when she awakes in a panic and pushes Ted down the stairs we don't see his face or Lucy until after the fact. When she breaks the window on the black SUV, when she hears the pine cones hitting her window at night... she is alone.
I think we as an audience just weren't offered a way to tie our own questions with Martha's state of mind. Maybe if there was a scene in which Martha asks these same questions to Lucy. Maybe if they shot from a first-person perspective. I don't know but it just didn't quite work for me.