Natalie Wood Saw Robert Wagner & Christopher Walken Having Sex Just Before She Died

Long lost documents from the Natalie Wood death investigation have been recovered by The Enquirer. Part of the documents include notes from a log of lifeguards that was submitted to police as a part of the searching for the body of Natalie Wood. The log states in part that detectives were working on a theory that Natalie Wood had walked in on Robert Wagner and Chirstopher Walken having sex just prior to the death of Natalie Wood. It is not that I don't believe the story, but I'm not sure how that would lead to the argument and death. If Wagner and Walken were having sex on the boat, chances are they had sex before and Natalie probably would have known about it. Would her discovering them be enough to cause an argument and get her tossed overboard?