that’s the thing though ,she starts TLJ in a place of doubt , " I need someone to show me my place in all this ." In the end ,she has cast that doubt aside .She literally has no time to doubt or question her abilities in the moment where she lifts the rocks or people will die . I am not sure what you meant by it happens off screen . If you are referring to her thoughts , I suppose that could be the case but I don’t see how that is relevant . other than comparing it to Luke expressing doubt about lifting the x-wing . And having her use two hands would be to weaken her character in my opinion .